Paint Coverage Calculator
Rounding Up Is the Whole Point
Paint doesn't sell in fractional gallons, so a coverage calculation that comes out to 2.3 gallons is really a 3-gallon purchase — buying short means an interrupted job and a mismatched-batch risk on the touch-up can. This calculator does the area math and then rounds up to the nearest whole gallon, which is the number that actually matters at checkout.
The Formula
Coverage per gallon defaults to 350 sq ft, a commonly cited average for interior latex paint on a primed, smooth wall — textured or porous surfaces reduce actual coverage.
Where This Calculation Matters
- Buying the right amount the first time — a mid-project trip back to the store rarely gets you paint from the exact same batch, risking a visible sheen or tint difference.
- Budgeting multi-coat jobs accurately — a color change or a dark-to-light repaint often needs two full coats, doubling the paint requirement versus a single-coat touch-up.
- Comparing coverage claims — premium paints often claim higher coverage per gallon than budget lines; running both through the same formula shows the real gallon-count difference.
- Estimating total job cost — once gallons are known, multiplying by price per gallon turns a wall measurement directly into a materials budget.
Gallons Needed by Wall Area
At the default 2 coats and 350 sq ft/gallon coverage:
| Wall area | Total paintable area (2 coats) | Gallons needed |
|---|---|---|
| 200 sq ft | 400 sq ft | 2 |
| 400 sq ft | 800 sq ft | 3 |
| 600 sq ft | 1,200 sq ft | 4 |
| 800 sq ft | 1,600 sq ft | 5 |
Notice the jump isn't linear — 600 sq ft needs 4 gallons while 800 sq ft only needs one more, because each gallon's leftover capacity carries into the next tier before a new gallon is required.
How to Use This Calculator
- Enter the Wall Area (sq ft) to be painted.
- Enter the Number of Coats (defaults to 2).
- Adjust Coverage per Gallon if your paint's label states a different figure than the 350 sq ft default.
- Optionally enter Cost per Gallon to see the total materials cost alongside the gallon count.
- Select Calculate to see the gallons needed, rounded up to a whole number.
Related Calculations
Painting as part of a larger project? Budget the full job with the Remodeling Cost Calculator, or size a wallpaper alternative with the Wallpaper Calculator.