Paint Calculator
Estimate paint needed from wall area and coverage rate.
Plan your painting project
Measure rooms or surfaces, subtract openings, and estimate paint, primer, labor and total cost.
1Choose what you are painting
2Enter measurements
3Paint and project details
Check the label; 350–400 ft² per gallon is common.
Adjust any measurement to update the entire estimate.
How to calculate paint
This calculator estimates how many gallons of paint you need based on the total wall area and your paint's coverage rate — the number that determines how many cans to buy so you don't run out mid-project or overspend on paint you won't use.
How the calculation works
Gallons needed = Wall area (sq ft) ÷ Coverage per gallon (sq ft). Paint cans list their coverage rate (commonly around 350–400 sq ft per gallon for one coat), and dividing your total area by that rate gives the gallons required for one coat.
Example
A room with 420 sq ft of wall area, using paint rated for 350 sq ft/gallon coverage: Gallons needed = 420 ÷ 350 = 1.2 gallons for one coat. Since most interior painting uses two coats for even color, double this to about 2.4 gallons total — in practice, that means buying one gallon plus a quart, or two full gallons to have leftover for touch-ups.
Frequently asked questions
How many coats of paint do I actually need?
Most interior painting uses two coats for even, opaque color, especially over a different existing color. A single coat may suffice for touch-ups or when painting a very similar shade over the existing color.
Does ceiling area count separately from wall area?
Yes — ceilings typically use a different paint (flat ceiling paint) and should be measured and calculated separately from wall area, even though the same coverage-rate formula applies to both.
Paint Calculator
Gallons needed = Wall area (sq ft) ÷ Coverage per gallon (sq ft). Paint cans list their coverage rate (commonly around 350–400 sq ft per gallon for one coat), and dividing your total area by that rate gives the gallons required for one coat.
Let's understand your paint result.
Calculate a result above and this guide will help you interpret it using this calculator's own formula and explanation.
Pro Tips for Paint
- This calculates one coat — multiply by 2 for a standard two-coat paint job, which is typical for most interior walls, especially with a color change.
- Check the specific coverage rate on your paint can rather than assuming a standard number — it varies by paint brand, sheen, and whether you're painting over a similar or very different existing color.
- Round up to the nearest full gallon or quart when buying — leftover paint is useful for future touch-ups, and running short mid-project to find the exact same color again can be frustrating.
Common Paint Mistakes to Avoid
- Forgetting to subtract door and window area from your wall area for large window walls — for most rooms this is a small enough difference to ignore, but a wall with a big picture window or sliding door can meaningfully overestimate paint need if not adjusted.
- Assuming primer and paint have the same coverage rate — primer often covers differently, and if you're priming bare drywall or a big color change, check the primer's specific coverage separately.
When to Use This Calculator
This calculator estimates how many gallons of paint you need based on the total wall area and your paint's coverage rate — the number that determines how many cans to buy so you don't run out mid-project or overspend on paint you won't use.