Chapter 02Paint · Problem-solving guide
How much paint do I really need, and why did I run out?
Measure the wall area, take out the doors and windows, multiply by the number of coats and divide by the coverage on the can. Sherwin-Williams' calculator uses 350 sq ft per gallon for walls, and Benjamin Moore lists 400 to 450 for Regal Select, both for one coat. Paint usually runs out halfway for one of two reasons: it was bought for one coat, or the label figure was used on a rough wall that takes more.
Source: Sherwin-Williams paint calculator, checked October 10, 2026; Benjamin Moore Regal Select (matte) product page, checked October 5, 2026; Sherwin-Williams painting FAQs, checked October 17, 2026.
- Wall to paint in a 12 x 14 ft bedroom372 sq ft Arithmetic from the figures on this page
- One coat at 350 sq ft per gallon1.06 gal Sherwin-Williams paint calculator, October 10, 2026
- Two coats at 350 sq ft per gallon2.13 gal Sherwin-Williams paint calculator, October 10, 2026
Why paint runs out
The coverage on a can is for one coat on a smooth, sealed wall. Sherwin-Williams calls a 400 sq ft per gallon figure theoretical, because it leaves out the texture of the wall and the paint that stays on the roller, the tray and the brush.
Source: Sherwin-Williams painting FAQs, checked October 17, 2026.
- A gallon bought for 372 sq ft of wall covers it once. The second coat needs the same amount again.
- Texture, porous plaster and unpainted drywall soak up more paint than the label assumes.
- Paint left in the roller cover, the tray and the brush never reaches the wall.
- Floor size is the wrong number. A 12 x 14 ft floor is 168 sq ft, but its walls are 416 sq ft before the door and windows come out.
Source: Sherwin-Williams painting FAQs, checked October 17, 2026.
Work out what to buy, step by step
Measure the walls
Add up the wall widths along the floor and multiply by the ceiling height. In a 12 x 14 ft room with 8 ft walls that is 52 ft × 8 ft = 416 sq ft.
Take out doors and windows
Multiply width by height for each one. One 3 ft x 6 ft 8 in door and two 3 x 4 ft windows come to 44 sq ft, which leaves 372 sq ft.
Find the coverage figure
Look on the can label or the product's data sheet for square feet per gallon. No label to hand? Work at both ends of the published band, 350 and 450 sq ft per gallon.
Multiply by the coats
Two coats double the area to paint: 372 × 2 = 744 sq ft.
Divide, then round up
744 ÷ 450 = 1.65 gallons and 744 ÷ 350 = 2.13 gallons. Buy for the higher figure, rounded up to the next quart: 2 gallons and 1 quart.
Source: Sherwin-Williams paint calculator, checked October 10, 2026; Benjamin Moore Regal Select (matte) product page, checked October 5, 2026.
Ran out halfway? What to do now
- If you can, finish the wall you are on and stop where two walls meet. A small change in color is much harder to see across a corner than in the middle of a wall.
- Take the old can to the store. Its label has the color name, the code and the base; copy them onto the paint record so the new can is mixed to the same formula.
- Pour what is left of the old can into a bucket with the new paint and stir, so any small difference in tint spreads over the whole wall.
- Run the calculator again on just the unpainted walls and the coats still to go.
Write it down this time
Fill in the paint record before the receipt goes in the trash: brand, color code, batch number and where the leftover can lives.
Checklist to print
Fill this in before you go to the store or order online:
- Wall widths added up, and the ceiling height measured
- Doors and windows measured and taken out
- Coverage figure found on the can label or data sheet
- Number of coats decided
- Higher figure rounded up to the next quart
- Primer worked out separately, if you need it
- Color name, code and base written on the paint record
- Cans mixed at the same time, or a bucket ready to mix them together
Tips and tricks
- Tip 01
Cut in before you roll
Brushing the edges of a whole wall first, then rolling it, helps the cut line blend into the rolled paint.
- Tip 02
Box the paint
Pour every can of one color into one bucket and stir. Small batch differences disappear.
- Tip 03
Save a jar for touch-ups
A small sealed jar of the final color, labeled with the room, is easier to use than reopening a full can.
- Tip 04
Count closets
Closet walls and the backs of doors are easy to forget, and they add up across a house.
- Tip 05
Check the label before the second coat
Some labels list a wait time before the second coat. Rolling too soon can lift the first one.
What we would do
Plan for two coats and buy it all at once
Measure the walls, take out the doors and windows, and run the paint calculator for two coats at the low end of the coverage figure. Buy every can of one color on the same trip and mix them together. If you run short anyway, take the lid with its mixing label to the same store.
Questions
How many square feet does a gallon of paint cover?
It depends on the product and the wall. Sherwin-Williams' calculator uses 350 sq ft per gallon for walls, and Benjamin Moore lists 400 to 450 for Regal Select. Both are one-coat figures for a smooth surface.
Source: Sherwin-Williams paint calculator, checked October 10, 2026; Benjamin Moore Regal Select (matte) product page, checked October 5, 2026.
Is one gallon of paint enough for a bedroom?
For one coat on a small bedroom, sometimes. For two coats, rarely. The 12 x 14 ft bedroom on this page has 372 sq ft of wall, so two coats need 1.65 to 2.13 gallons at 350 to 450 sq ft per gallon.
Source: Sherwin-Williams paint calculator, checked October 10, 2026; Benjamin Moore Regal Select (matte) product page, checked October 5, 2026.
Why did my paint run out before the second coat?
The second coat needs as much paint as the first. If you bought enough to cover the wall area once, you bought for one coat.
Can I mix two cans of the same color?
Yes. Pouring cans of the same product and color into one bucket and stirring evens out small tint differences between them.
Should I count the ceiling?
Only if you are painting it. Sherwin-Williams' calculator uses 400 sq ft per gallon for ceilings, so work it out separately with that figure or the one on your label.
Source: Sherwin-Williams paint calculator, checked October 10, 2026.
Part of a system
This page is one part of a bigger job. The system page puts the parts in order.
SystemHome records binder: your house manualSix tabs for the facts a house keeps asking for: appliances and warranties, filter sizes, paint colors, measurements, manuals and service visits.8 steps · 6 parts · 1 page to printOpen the system
SystemRoom repaint: measure, buy once, record the colorCheck the year the home was built, measure the room, buy each color in one trip, log every coat and record the paint before the can goes on the shelf.8 steps · 4 parts · 1 page to printOpen the system
The tool and more guides
Chapter 02Paint coverage calculatorWork out how many gallons of paint a room needs from its size, doors, windows and coats, using coverage figures published by paint makers.Open the tool- Know-howOne coat or two? Reading the coverage line on a paint canThe coverage on a can is square feet per gallon for one coat. Two coats double the paint. When one coat can do, and what a second costs in a bedroom.Read the guide
- Know-howHow much paint for a ceiling, trim and doorsMeasure a ceiling, baseboards, casings and doors in square feet, then turn them into gallons and quarts. With a 12 x 14 ft bedroom worked through.Read the guide
- Chapter 02All paint toolsPaint quantity tools built on coverage figures published by paint makers, plus a printable record of colors, codes and leftover cans.Open the chapter
Sources
- Paint Calculator, Sherwin-Williams. Checked October 10, 2026.
- Regal Select Interior Paint - Matte, Benjamin Moore. Checked October 5, 2026.
- Painting FAQs, Sherwin-Williams. Checked October 17, 2026.
Every outside number on this page names its source and the date we checked it. See them all on the sources page. Spotted an error? Tell us.