40 m² with two coats
40 × 2 ÷ 10 × 1.10 = 8.8 L
Assume one-coat coverage of 10 m²/L and a 10% allowance. At 2.5 L per container, buy 4 containers, totalling 10 L. The surplus beyond the estimate is 1.2 L.
Home projects
Paint Calculator
Estimate paint from the surface area, number of coats, and your product's coverage. See the whole containers needed and the planned surplus.
Estimate paint quantity
Paint including allowance
Enter your area, coats, coverage, and container size, then select Calculate.
- Total area
- Net area to paint
- Paint before allowance
- Whole containers needed
- Purchase quantity
- Surplus beyond the estimate
Calculation steps
≈ marks display rounding. Calculations run in your browser. Press Enter to calculate. Successful results appear in this tab's Recent calculations.
Paint estimates with clear assumptions
A 5 m × 4 m room, 2.5 m high
2 × (5 + 4) × 2.5 = 45 m²
Subtract 5 m² of openings to leave 40 m². With two coats at 10 m²/L and no allowance, the estimate is 8 L. Adding the 20 m² ceiling gives 60 m² net and requires 12 L under the same assumptions.
700 ft² at 350 ft² per US gallon
700 × 2 ÷ 350 = 4 US gal
For two coats and no extra allowance, the estimate is 4 US gallons. With 1 US gallon containers, that is 4 containers. The coverage rates in these examples illustrate the arithmetic; they are not recommendations for a particular paint.
Formulas, units, and estimate limits
For a rectangular room, wall area is 2 × (length + width) × height. A flat ceiling adds length × width. Subtract the excluded area once, then multiply the remaining area by the number of coats. Divide by the product's coverage per coat to get paint before allowance. Multiply by (1 + allowance ÷ 100) to include extra paint.
Divide the paint requirement including allowance by the container size and round upward to a whole number. Purchase quantity equals that whole count multiplied by the container size. Surplus is purchase quantity minus the paint requirement including allowance. The calculator does not combine different container sizes or optimize prices.
Metric inputs use metres, square metres, litres, and square metres per litre. US customary inputs use feet, square feet, US liquid gallons, and square feet per US gallon. A US gallon is not an imperial gallon. Changing the system relabels the fields without converting their values; enter all values in the selected system before calculating.
Dimensions, total area, coverage, and container size must be positive. Excluded area must be nonnegative and smaller than total area. Coats must be a whole number from 1 to 10; extra allowance must be from 0 to 100%. Blank excluded area and allowance mean zero. Inputs support at most 64 characters, 15 integer digits, and 10 decimal places. Expressions, scientific notation, and embedded units are not accepted. Inactive fields are ignored.
Arithmetic retains exact fractions. Only displayed decimals are rounded, with halfway values rounding away from zero and trailing zeros omitted. ≈ marks a rounded display. The number of containers uses the exact requirement even when the visible paint amount rounds down to a container boundary. More displayed digits do not improve the accuracy of your measurements or coverage estimate.
Calculate different products, primers, colors, surfaces, or coat counts separately. This estimate assumes uniform coverage on the included surfaces; it does not model textured or porous materials, application losses, unusual wall shapes, sloped ceilings, surface preparation, or product-specific film thickness. Actual usage can differ from the result.
Reference: Sherwin-Williams — paint calculator and project estimating guidance. Follow the coverage and application instructions for the product you will use.
Common questions
What coverage should I enter?
Enter a one-coat coverage value appropriate for your chosen product and surface, using its label or technical instructions. If a range is given, choose the value that fits your project or compare both ends of the range. There is no single coverage rate that suits every paint and surface.
Should I subtract windows and doors?
Subtract surfaces that will not use this paint. Enter the combined excluded area in the same units as the total area. If your area measurement already excludes them, do not subtract them again.
Does extra allowance include a second coat?
No. Number of coats is a separate input. Extra allowance is a percentage added after the paint for all coats is calculated. If the coverage value you have describes a complete two-coat system, check the product instructions before using it as one-coat coverage.
Why can the container count seem higher than the displayed estimate?
The visible amount may be rounded. A requirement of 5.000000001 L can display as approximately 5 L, but it still exceeds two 2.5 L containers. The exact requirement therefore gives three containers. This prevents display rounding from understating the purchase quantity.
Will the surplus equal the paint left at the end?
Not necessarily. Surplus here is the amount purchased above your estimate including allowance. Some allowance may remain unused, or actual coverage and losses may use more paint than expected.