Windows Errors? Fix Them Before They Spread
Recommended Free Tools
Outbyte PC Repair · freeRepair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.
Fix My PC Now →ThatPainter is reader-supported. When you buy through links on our site, we may earn an affiliate commission. Learn More
For a typical smooth room, plan on one gallon of Sherwin-Williams paint covering about 350–400 square feet for one coat. To estimate your order, measure the walls, subtract doors and windows, multiply the remaining area by the number of coats, divide by the coverage printed on your can, and round up to whole cans. A 12 × 12-foot room with 8-foot walls, one standard door and one standard window needs about 2 gallons for two wall coats when calculated conservatively at 350 square feet per gallon.
Use Sherwin-Williams’ Quick Calculation mode for a simple ballpark. Choose Custom Calculation when the room includes a ceiling, baseboards, crown molding, window trim, texture or other details. The calculator is an estimate, so check the product label and confirm a large order with a Sherwin-Williams store representative.
As an Amazon Associate I earn from qualifying purchases.
How much area does a gallon of Sherwin-Williams paint cover?
Sherwin-Williams typically cites 350–400 square feet per gallon of finish paint, about 100 square feet per quart, and 200–300 square feet per gallon of primer. Those are planning ranges rather than guarantees. The exact product label, surface condition, color change, number of coats and application method determine how far a can actually goes.
For a cautious estimate, use 350 square feet per gallon. If the wall is smooth, sealed and close in color to the existing finish, the product may perform nearer the upper end of the range. Porous, patched or textured surfaces, a dark-to-light color change and additional coats can push consumption higher. Never substitute a generic coverage number for the coverage printed on the specific can.
Popular on Amazon
- COMPLETE 5-PIECE BRUSH SET FOR EVERY PAINTING TASK — Includes 1 Inch Flat, 1.5 Inch Angle, 2 Inch Flat, 2 Inch Angle Stubby, and 2.5 Inch Angle brush giving you every size professional painters use daily. Get all 5 for less than the price of a single brush from hardware store brands — professional grade performance at a fraction of the cost. Perfect for walls, trim, cabinets, doors, furniture, and detailed cutting-in work on any project.
- ZERO BRISTLE LOSS — GUARANTEED BY PRECISION ADHESIVE BONDING — Every bristle is locked in place with precision-set adhesive that keeps them in the brush — not in your paint job. The coated steel ferrule provides structural support while the adhesive bond ensures clean performance on every stroke. Premium SRT synthetic filaments load more paint and release it evenly for a smooth streak-free finish on walls, ceilings, and trim. Works with latex, oil-based paint, primer, sealer, and wood stain.
- INCLUDES THE ANGLE STUBBY MOST SETS LEAVE OUT — Professional painters know the 2 Inch Angle Stubby is the go-to brush for tight cabinet interiors, window sashes, inside corners, and detailed trim where standard angle brushes are too long. Combined with the 1.5 and 2.5 inch angle sash brushes you have precision cutting-in covered at every scale — baseboards, crown molding, door casings, and ceiling lines.
- FLAT BRUSHES FOR BROAD SMOOTH COVERAGE ON ANY SURFACE — The 1 and 2 inch flat brushes deliver even coverage on walls, furniture, shelving, doors, fences, decks, and wood surfaces. Ideal for applying primers, stains, varnishes, polyurethane, and specialty coatings. Solid wood handles provide all-day comfort and control for both professional contractors and weekend DIY homeowners tackling interior or exterior painting projects.
- TRUSTED BY PROFESSIONAL PAINTERS AND CONTRACTORS NATIONWIDE — Pro Grade delivers professional-grade results at a price that makes sense for crews who go through brushes on every job. Ideal for property managers, remodeling contractors, apartment turnover crews, maintenance teams, and commercial painting operations. Backed by thousands of verified reviews from working painters. Washable and reusable for multiple projects.
Coverage conversions
- Finish paint: approximately 350–400 square feet per gallon.
- Quart: approximately 100 square feet, subject to the product label.
- Primer: approximately 200–300 square feet per gallon.
Coverage is calculated per coat. If a product covers 350 square feet for one coat and you apply two coats to 350 square feet of wall, you have 700 square feet of applied coverage to account for, not 350.
What measurements do you need before calculating?
Record each wall length, the wall height, the number of doors and the number of windows. Sherwin-Williams’ Pro Painters Institute worksheet also asks for the room’s length and width, which you need for a ceiling calculation.
Measure the walls
- Measure the length of every wall in feet. For a rectangular room, you can add the four wall lengths or use
2 × (room length + room width). - Measure the actual paintable height from floor to ceiling. Use the lower height for a room with a consistent soffit, or split the wall into separate rectangles when heights vary.
- Count doors and windows. If their sizes differ substantially from standard openings, measure each one instead of using the representative deductions.
Identify separate surfaces
Decide whether the ceiling, baseboards, crown molding, window trim and doors will be painted. Calculate each surface separately when it uses another color, sheen or product. A dedicated ceiling product has its own coverage, so do not apply the wall paint’s number automatically.
How do you calculate wall paint by hand?
The manual method is reliable for a rectangular room and makes the assumptions behind any calculator result visible. Use the conservative 350-square-foot coverage figure when you do not yet know the product’s label coverage.
- Calculate gross wall area. Add the wall lengths and multiply by wall height:
(wall 1 + wall 2 + wall 3 + wall 4) × wall height. - Subtract openings. As representative worksheet assumptions, subtract 21 square feet for each standard door and 15 square feet for each standard window. Use measured areas for oversized, narrow, grouped or unusually shaped openings.
- Add a ceiling only if it will be painted. For a rectangular room, use
room length × room width. Keep this area separate if the ceiling uses a different product. - Multiply by the number of coats. Two coats means multiplying the paintable area by two. A one-coat example on smooth, flat, nonporous surfaces should not be treated as a promise that one coat will hide every color or repair.
- Divide by product coverage. For conservative planning, use
paintable area × coats ÷ 350. If the can specifies a different coverage, use that number instead. - Round up. Buy whole cans and round up to the next gallon. Sherwin-Williams recommends rounding up to help ensure coverage and keeping leftover paint for future touch-ups.
Worked wall formula
Suppose four walls total 48 linear feet, the wall height is 8 feet, and the room has one standard door and one standard window. Gross area is 48 × 8 = 384 square feet. After representative deductions, paintable area is 384 − 21 − 15 = 348 square feet. For two coats at 350 square feet per gallon, the estimate is 348 × 2 ÷ 350 = 1.99 gallons, so buy 2 gallons.
How much paint does a room need? Room-by-room examples
The examples below use two wall coats, 350 square feet per gallon, one 21-square-foot door and one 15-square-foot window unless noted. They are transparent planning calculations, not a product-specific quote. Ceiling amounts assume the same paint is used and are rounded separately.
Outdated Drivers Are Slowing You Down
One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchPC Slower Than It Used to Be?
A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11| Room example | Wall-area arithmetic before coats | Approximate wall paint for two coats | Ceiling if painted with the same product |
|---|---|---|---|
| 10 × 10 ft, 8-ft walls, 1 door + 1 window | 320 − 21 − 15 = 284 sq ft | 2 gal | 100 sq ft ceiling: 1 gal |
| 12 × 12 ft, 8-ft walls, 1 door + 1 window | 384 − 21 − 15 = 348 sq ft | 2 gal | 144 sq ft ceiling: 1 gal |
| 12 × 16 ft, 8-ft walls, 1 door + 1 window | 448 − 21 − 15 = 412 sq ft | 3 gal | 192 sq ft ceiling: 2 gal |
| 15 × 20 ft, 9-ft walls, 2 doors + 3 windows | 630 − 42 − 45 = 543 sq ft | 4 gal | 300 sq ft ceiling: 2 gal |
Notice that the ceiling is not included in the wall gallon figure. In the 12 × 12-foot example, the walls require about 2 gallons for two coats and the 144-square-foot ceiling adds about 1 gallon when the same coverage assumption is used.
Also popular on Amazon
- Great Value Pack Artist Paint Brushes: Soucolor 20 brushes in 10 sizes professional paintbrushes set — no shedding, holds paint well, cleans easily, Acrylic, watercolor, oil, gouache, Halloween pumpkin decoration & face painting, rock painting, ceramics. Fantastic high quality gifts for creative, artistic siblings to share!
- Awesome Set of Paint brushes: Professional paint brushes can cover all of your needs. The multi-purposed brushes are ideal for Watercolor, Oil, Gouache, enamel, Acrylic Painting, Body, Nail, Face Painting, Miniature, Model, Wood, Glass, Cup, Ceramic, Fine work, Art class, Craft Art Painting, DIY Art Crafts etc.
- Soft and long-lasting: The bristles are soft and strong, with nickel metal ferrules and blue wooden handles. After cleaning, the bristles will become soft and fluffy again and will not fall off.
- Easy to clean: it’s very convenient to Wash well in soap and water. Retain shape after drying. the brushes hold up very well. Nice selection to beginners and professionals. Keep them clean and they last a long time.
- Halloween Pumpkin Ceramic Crafts Supplies: A Great painting gift for family, friends, kids, girls, women, student, classmate, teacher. For using in school, travel or used in the home and office.
Should you use Quick Calculation or Custom Calculation?
Quick Calculation is appropriate for a simple room or a single statement wall when you need a fast ballpark. Custom Calculation is the better choice when room details materially change the paintable area.
Quick Calculation
Choose this mode when the room has straightforward dimensions, standard openings and no need to model trim or multiple surface types. Enter the basic room measurements and use the result as an initial shopping estimate.
Custom Calculation
Use Custom Calculation when you need to represent ceilings, baseboards, crown molding, window trim, wall texture or other features. Entering more of those details makes the estimate more realistic because the calculator can distinguish surfaces that the simple mode treats as one rectangle.
Deck Calculation
Use Deck Calculation for a porch or deck rather than an interior room. Exterior boards, railings and other deck components have different surface areas and conditions from interior drywall, so an interior-room calculation is not the right starting point.
Sherwin-Williams notes that requirements vary with application method and surface type or condition. Treat any calculator output as an estimate and ask a local store representative to verify quantities before a large purchase.
How do two coats, texture and color changes affect the estimate?
Two coats double the calculated application area, but the final gallon count can rise further when the surface absorbs paint or the new color has poor hiding over the old one.
Number of coats
Use the coverage number for one coat, then multiply the paintable area by the planned coats. A two-coat plan is not interchangeable with a one-coat plan simply because the room’s square footage is unchanged. Follow the product label and the finish appearance you need.
Free tools Windows power users keep installed
One-click scans. No signup required.
Also popular on Amazon
- 【All sizes of art brushes】: The 10 sizes of multi-functional brushes have various shapes, making the mixing color easier, which is very suitable for artists, students, teenagers, children and painters at all levels. Wonderful Present ideas for friends and family who like painting!
- 【general brush set】: Professional paint brush can meet all your needs. Multifunctional brush is very suitable for watercolor, oil, gouache, acrylic painting, body, nail, face painting, miniature, model, ceramics, arts and crafts painting, etc.
- 【high quality process】: It is designed with anti falling bristles, anti-rust nickel ferrule and solid wood handle. You can use the brush to focus on the painting and always be creative.
- 【easy to maintain】: After using the brush, it is very convenient to clean the brush with warm soapy water and reshape the tip of the brush. Air dry the brush and place it on top of the top for long use.
- 【100% satisfaction guarantee - buy now】1 packs of set brushes, you can also get friendly customer service, any questions feel free to contact us, within 24 hours to help you! There is no risk in buying our paint brush kit.
Texture and porosity
Textured, patched or porous walls expose more surface and can consume more paint than a smooth, sealed wall. If the wall condition is uncertain, use the conservative end of the coverage range and allow for a possible additional coat rather than ordering to the optimistic figure.
Dark-to-light changes
A major color change can require primer and additional finish coats. Sherwin-Williams’ DIY handbook identifies new drywall and dark-to-light changes as situations where primer can improve adhesion and reduce the number of finish coats needed. A sample applied to the actual wall can reveal whether the planned finish color is hiding adequately.
How much primer do you need?
Plan on approximately 200–300 square feet per gallon of primer, then check the primer can for its product-specific coverage. Because primer generally covers less area per gallon than finish paint, do not divide a primer area by the finish-paint number.
When primer is especially useful
- New drywall, where a suitable primer helps create a more uniform surface.
- Dark-to-light color changes, where primer can improve the transition and reduce the number of finish coats.
- Patched or porous areas that would otherwise absorb finish unevenly.
Calculate primer for the surfaces that need it, not automatically for every surface in the room. If only repaired sections require spot priming, measure those sections and follow the product instructions.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
How should you calculate ceilings, trim and doors?
Keep ceilings, trim and doors separate from wall paint whenever they use a different product, sheen or color. This prevents a wall estimate from hiding a second purchase.
Ceilings
For a flat rectangular ceiling, multiply room length by room width. Multiply that area by the number of coats and divide by the ceiling product’s coverage. If the ceiling is vaulted, tray-shaped or interrupted by open sections, divide it into rectangular or triangular sections and add the areas.
Baseboards and crown molding
Custom Calculation can represent these features. If you calculate manually, measure their length and average paintable height or width, then treat each as a separate rectangle. Include both sides only when both sides will actually be painted.
Also popular on Amazon
- Bates paint brushes come in a convenient 6 pieces with 3 flat and 3 angled bristle styles, including (1”, 1.5”, 2”) flat and (1.5”, 2”, 2.5”) angled bristles, perfect for tackling any surface painting or staining job.
- The sturdy natural bristles of each brush are designed to hold more paint, creating a smoother finish with fewer streaks and saving you time on the job.
- The lightweight wooden handles provide extra comfort and ease during long painting processes like walls, trims, cabinets, and doors.
- These versatile brushes are ready-to-use, easy to clean, and can be reused multiple times, making them economical as well as reliable tools for any painting project.
- Bates paint brushes can be used for both oil-based paints as well as latex stains and are ideal for home or commercial projects such as decks, fences or DIY painting jobs.
Doors and window trim
The 21-square-foot door and 15-square-foot window figures are representative deductions for wall area, not universal measurements for painting the doors or trim themselves. Measure the actual trim and door faces when those surfaces will receive paint, especially if they use another sheen.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsDoes sheen change how much paint you should buy?
Sheen primarily determines the product and finish you choose, so coverage must be checked for that exact product rather than borrowed from another sheen.
- Semi-gloss: Sherwin-Williams describes it as washable for frequently cleaned rooms such as kitchens and bathrooms.
- Satin: Suitable for high-traffic areas according to Sherwin-Williams’ finish guidance.
- Flat or matte: Useful for hiding surface imperfections.
Because sheen, color and product line can change coverage, do not combine gallons of different products in one calculation without checking each label. If walls, trim and ceiling use different finishes, calculate and purchase them as separate line items.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What supplies help you use the paint estimate successfully?
The quantity calculation is only useful if the paint can be applied evenly and the surrounding surfaces are protected. Sherwin-Williams identifies a roller and brush kit as core equipment: rollers cover broad areas, while brushes reach corners and fine spaces.
- Roller and brush kit matched to the surface.
- Painter’s tape for clean edges.
- Drop cloths to protect floors and furnishings.
- Patching compound and appropriate tools for repairs.
- Primer when the surface or color change calls for it.
- A color sample to check hiding and appearance on the actual wall.
Prepare and repair before finalizing the order. A wall that becomes more porous after sanding or patching may need more product than an initially smooth measurement suggests.
Quick wins for a faster PC:
Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →What are the most common paint-calculation mistakes?
Most overages and shortages come from mixing surfaces or assumptions rather than from the multiplication itself.
Using room floor area as wall area
Floor area alone ignores wall height. For walls, use perimeter multiplied by height, then subtract openings.
Also popular on Amazon
- 2 Inch Angled Paint Brush for Precision Cutting-In – Designed for clean, sharp lines around trim, baseboards, ceilings, corners, and detailed edge work. The perfect size for control and coverage.
- Value 3-Pack for Pros & DIY Projects – Includes three professional 2-inch angled sash brushes — ideal for contractors, remodelers, and homeowners tackling multiple rooms or repeat paint jobs.
- Smooth Results on Walls, Trim & Cabinets – Great for interior wall painting, cabinet edges, furniture projects, and trim work where a smooth finish and crisp control matter most.
- Works with Latex Paint, Oil-Based Paint & Stains – Premium synthetic filaments hold more paint, reduce streaks, and provide a clean finish with latex paints, oil coatings, and wood stains.
- Works with Latex Paint, Oil-Based Paint & Stains – Premium synthetic filaments hold more paint, reduce streaks, and provide a clean finish with latex paints, oil coatings, and wood stains.
Forgetting the second coat
Enter the actual number of coats before dividing by coverage. A one-coat estimate will understate a two-coat project.
Subtracting standard openings when they are not standard
The worksheet deductions are representative. A wide sliding door, grouped windows or a small transom should be measured so the deduction reflects the real opening.
Combining the ceiling with the walls
Ceilings add area and often use another product. Keep the ceiling calculation separate so you can buy the correct color and sheen.
Rounding down
Never turn 2.1 gallons into 2 gallons. Round up to whole cans; the extra paint also provides a consistent batch for touch-ups.
Trusting a calculator without checking the label
The calculator cannot know every product’s coverage or every wall’s condition. Compare its result with the can label and confirm unusual or large projects with a store representative.
What should you verify before placing the order?
- Confirm room length, width and every wall height.
- Check door and window counts and replace representative deductions with measured areas when needed.
- List walls, ceiling, trim and doors separately by color, sheen and product.
- Set the number of coats for each surface.
- Read the exact coverage on each can and use the conservative figure when the surface is uncertain.
- Calculate primer separately at its own coverage rate.
- Round each result up to whole cans.
- Have a Sherwin-Williams store representative review the quantities for a large or complicated project.
Frequently Asked Questions
Can I use one gallon of paint in two different rooms?
You can divide a combined paintable area across rooms only when the same product, color, sheen and number of coats apply. Add both rooms’ areas first, divide by the can’s coverage, and round the combined result up; otherwise calculate each product separately.
The Tool Desk
Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →How do I estimate paint for a room with different wall heights?
Split the walls into sections with the same height, calculate each rectangle, subtract openings from the section where they occur, and add the remaining areas. This avoids applying one average height to a wall that includes a soffit or other step-down.
When is a quart more practical than a gallon?
A quart is useful for a small measured area or a touch-up when the product label’s coverage supports it. Sherwin-Williams cites about 100 square feet per quart, but the label and the amount of paintable surface should determine whether a quart is sufficient.
Why can the same room need different gallon counts with different paints?
Coverage varies by product, sheen, application method and surface condition. A wall estimate made with a 350-square-foot planning value must be recalculated if the selected can lists another coverage or if the surface requires primer or extra coats.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
