How much paint do you need for a room?
Measure each wall or ceiling as a separate rectangle. Subtract openings that will not receive paint, enter the number of coats for that surface, and repeat for the remaining surfaces. Enter the coverage per US gallon printed for your actual paint. The worksheet reports net surface area, total coated area, calculated gallons, and whole containers. It estimates paint only, not primer, trim, labor, or exterior siding.
What formula converts wall area into gallons of paint?
For each surface, multiply length by height or width and subtract measured openings. Multiply that net area by its coat count. Add coated areas across all surfaces, then divide by the manufacturer’s stated coverage in square feet per US gallon. An optional planning allowance applies after the base calculation; whole cans are rounded up only after the allowance.
Paint (US gal) = Σ[(length × height − openings) × coats] ÷ coverage per US gal
Order volume = calculated paint × (1 + allowance ÷ 100)
Containers = ceiling(order volume ÷ container size)
How do you measure doors, windows, and other openings?
Measure an opening’s width and height, multiply them, and enter their combined area in the same units as the selected surface. An opening must be smaller than the wall it is subtracted from. Do not deduct doors or windows when their trim or panels will be painted with the same product. For a room with several walls, use one row per surface so the openings and coat counts stay auditable.
How many coats should you include?
Choose the number of coats planned for each surface, from one to ten. A ceiling and walls can have different coat counts. Color changes, patching, porous surfaces, and manufacturer instructions can change the number required. Count primer as a separate product and estimate it in a separate worksheet using its own coverage. Avoid treating paint-and-primer marketing claims as a guarantee of one-coat coverage.
What coverage rate should you use per gallon?
Use the square-foot coverage on the chosen product label or data sheet. Coverage varies by paint, substrate, porosity, texture, application method, and film thickness. Sherwin-Williams describes roughly 350–400 sq ft per gallon as a typical planning range, while a particular Benjamin Moore interior product lists 400–450 sq ft per gallon. These examples are not defaults in the calculator; the coverage input stays blank until you supply a figure for your product.
What does a two-coat paint estimate look like?
Consider four 12 ft by 8 ft walls with no openings: 384 sq ft of surface. Two coats mean 768 sq ft of coated area. At an illustrative label coverage of 400 sq ft per US gallon, the base estimate is 1.92 gallons. A separate 10% allowance yields 2.112 gallons. With one-gallon cans, round up to three cans. If you instead select a five-gallon container, the worksheet returns one container; compare actual package choices and local prices before purchasing.
How do you estimate a ceiling or several rooms?
For a rectangular ceiling, use room length and width as the two dimensions and choose its own coat count. Add each room wall and ceiling as a separate row, up to 20 surfaces. If a different color or finish is used, calculate it separately so one combined total does not mix paint products. For an irregular room, divide the surface into rectangles without counting an overlap twice. Check the square footage calculator for a more detailed shape takeoff.
How should you choose can sizes and calculate cost?
Select a one-gallon, five-gallon, quart, or custom US-gallon container size. The worksheet rounds the required order volume up to whole containers of that one chosen size. Optional cost multiplies the can count by your entered price per container; it does not optimize a mix of package sizes or include taxes, tools, primer, delivery, or labor. Compare alternate container sizes by recalculating and adding each result to the in-page comparison list. Keep paint from different colors or products on separate worksheets.
How are metric measurements handled?
Switch feet to meters and the entered dimensions and opening areas convert, preserving the same physical surfaces. The coverage field remains in square feet per US gallon because it follows the selected product label. Results include square meters and liters for comparison; one US gallon equals 3.785411784 liters. If a label gives coverage only in m²/L, multiply that figure by 40.7458 to enter approximate sq ft per US gallon, or confirm the conversion with the manufacturer.
| Measure | Equivalent |
|---|---|
| 1 ft | 0.3048 m |
| 1 sq ft | 0.09290304 m² |
| 1 US gallon | 3.785411784 L |
When will this estimate differ from the final paint used?
Texture, unpainted openings, application loss, touch-ups, substrate absorption, and the actual number of coats can change consumption. A small room with contrasting colors may require separate quantities even if the total area is the same. Do a test section where coverage is uncertain, use the product’s technical data, and confirm package availability. For facade-specific measurement and openings, use the exterior paint calculator when it is available; the two project intents should remain separate.
