Calculation method
Subtract door and window area, multiply by coat count and allowance, divide by the label coverage per gallon, then round up to whole cans of the entered size.
Worked example: input to purchase quantity
Thirty feet (9.14 m) of 8 ft (2.44 m) wall gives 240 ft² (22.3 m²). Subtract 40 ft² (3.72 m²) of openings to get 200 ft² (18.58 m²). Two coats plus 10% equal 440 coat-ft² (40.88 coat-m²). At 350 ft² per gallon (8.6 m²/L) that is 1.257 gallons (4.76 L), requiring 2 one-gallon (3.79 L) cans.
Estimate paint from coat-area
Paint coverage is an area-per-volume claim, so a useful order must account for the wall surface, excluded openings, number of coats, and the coverage printed for the chosen coating. This calculator finds net wall area, multiplies by coats, adds a touch-up allowance, and divides by square feet per US gallon. It then rounds upward to full cans. The intermediate gallon requirement remains visible so you can compare one-gallon (3.79 L) and larger-container combinations.
Total wall length can be the sum of several walls that share one height and coating plan. Rooms with different heights are better calculated as separate groups and combined at the gallon stage. Measure large doors and windows; tiny openings can be left in the area because cutting-in and roller loss consume paint too. Never let deductions exceed gross wall area—the calculator rejects that condition because it signals a measurement or unit error.
Use realistic label coverage
Coverage varies with product, color, substrate texture, porosity, application method, and film thickness. Enter the manufacturer’s stated coverage for the exact coating rather than assuming a universal number. New drywall and repaired patches may absorb more unless properly primed. Rough masonry and textured surfaces expose more area than their flat projection. Spraying can introduce transfer loss that is not represented by a roller-oriented label range.
Coats are explicit because coverage for one coat does not make a two-coat finish. A dramatic color change, deep base, low-hide color, or uneven substrate may need a primer or additional finish coat. Primer is a separate product with its own coverage and can size; calculate it separately. Do not inflate finish paint waste to conceal a missing primer plan.
Select cans without false precision
The can-size field is in US gallons because common retail containers are marketed that way. In metric dimension mode, coverage may be entered as square metres per US gallon while can size remains the labelled US-gallon capacity. If your market sells litres, convert the container to US gallons or compare the computed gallon requirement with the label’s litre capacity. One US gallon is about 3.785 litres.
Rounding each room independently can create more surplus than combining rooms that use the exact same product, sheen, and color. Conversely, do not combine areas that require different coatings merely to produce a neat total. Tinted paint may have limited return options, and separate batches can vary slightly. For a large uninterrupted surface, buying and boxing compatible cans together helps color consistency.
What the estimate does not decide
This result does not choose sheen, verify surface compatibility, assess lead hazards, or specify preparation. Cleaning, curing, sanding, repairs, caulk, primer, ventilation, protective equipment, temperature, and recoat time all affect the job. Follow safety and technical data for the coating and substrate. Older painted surfaces may require regulated testing and work practices before disturbance.
Before purchase, recheck wall length totals, height changes, opening deductions, coat count, and label coverage. Keep enough matching paint for later touch-ups, but store only where the product label permits and local disposal rules are met. The transparent calculation makes an order defensible; a small test area and product instructions determine whether the finish system actually works.
For several rooms, record each net area before combining only the rooms that truly share one color and sheen. This small schedule prevents a leftover from one finish being counted as usable stock for another and makes later changes easy to recalculate.
Product and method reference
The external reference is provided to help verify product-specific planning context; its values are not copied into the calculator. Always use the current label for the material being purchased. Sherwin-Williams paint calculator.
Calculation and editorial review: October 29, 2026. Arithmetic runs in your browser; project inputs are not submitted to TwoCut.