Calculator 05 / Paint
Paint Calculator
Paint coverage is per coat, so the quantity is paintable area × coats ÷ the spread rate on the can, and then waste on top. Estimate gallons of paint needed for a room's walls, based on coverage rate and number of coats.
How this calculator works
Coverage rate is the figure on the can, and it is the number most worth questioning — it assumes a smooth, primed, non-porous surface and one coat. Anything rougher or thirstier than that drinks more paint than the label suggests. Primer is not counted here at all: it is a separate product with its own coverage rate, and it does not count as one of your coats.
Worked example: a 14 × 12 ft bedroom
Walls only, 8 ft ceiling, 40 sq ft of door and window to deduct, two coats at 350 sq ft per gallon, 10% waste:
- Perimeter = 2 × (14 + 12) = 52 ft
- Wall area = 52 × 8 − 40 = 376 sq ft
- Exact gallons = (376 × 2) ÷ 350 = 2.15 gal
- With 10% waste = 2.36 gal
- Rounded up = 3 gallons
Add the ceiling and the same room needs four. That single checkbox moves the order by a whole gallon, which is worth checking before you leave the shop rather than after.
Real coverage rates
The 350 default suits smooth, primed, previously painted drywall. Surfaces below that absorb more, and the difference is large enough to change the order. Use the figure for the surface you actually have.
| Surface | Sq ft per gallon | Notes |
|---|---|---|
| Smooth, primed or previously painted | 350–400 | The default assumption |
| Light texture (orange peel) | 300–350 | Common on newer drywall |
| Heavy texture (knockdown, popcorn) | 250–300 | More surface than it looks |
| Bare, unprimed drywall | 200–250 | Prime it instead — cheaper than paint |
| Masonry, block, stucco | 100–200 | Highly porous; block filler often needed |
| Primer, typical | 200–300 | Ordered separately from the finish coats |
Choosing a sheen
Sheen does not change how much paint you need, but it changes how the room reads and how it wears. The rule of thumb is that shine and washability rise together, and so does how mercilessly the finish shows every flaw underneath it.
| Sheen | Where it belongs | Trade-off |
|---|---|---|
| Flat / matte | Ceilings, low-traffic rooms | Hides defects; hard to clean |
| Eggshell | Living rooms, bedrooms | The usual compromise |
| Satin | Hallways, children's rooms | Wipeable; starts showing roller marks |
| Semi-gloss | Kitchens, bathrooms, trim | Durable; shows surface flaws |
| Gloss | Doors, cabinets, high wear | Toughest; needs the best prep |
Where paint orders go wrong
- Counting primer as a coat. It is a different product with a different coverage rate, and it is ordered separately. Two finish coats over primer means two, not one.
- Trusting the coverage on the can. That number is a best case on a smooth primed wall. Texture and porosity both eat into it.
- Buying gallons separately. Tint varies between batches. Buy the job at once and box it — pour all the cans into one bucket and mix — so the last wall matches the first.
- Deducting every opening. Cutting in around a window takes paint and time even though the glass takes none. Deduct the large openings and let the waste factor absorb the rest.
- Rounding down to save a gallon. Running out mid-wall leaves a lap mark that a second attempt will not hide, and the replacement gallon may not match.
Where these numbers come from
Spread rate varies more by product than by any general rule, so the manufacturer's own technical data sheet outranks this calculator every time. The rest is safety and air quality.
- EPA Renovation, Repair and Painting Rule — Required work practices when disturbing paint in housing built before 1978. A legal obligation, not a recommendation.
- EPA on volatile organic compounds — Why the VOC figure on the can matters in an occupied room, and how long to ventilate.
Do I need less paint for a second coat?
Usually not — a second coat covers the same area, so this calculator multiplies total area by the number of coats rather than reducing coverage for later coats.
What if I need less than a full gallon?
If your total comes in under a gallon, most stores sell quarts (¼ gallon) — round up to the nearest quart instead of buying a full gallon.
Can I save, share, or print a calculation?
Yes — use the Save, Copy link, and Print buttons under your results. Saved calculations can be grouped into a named project on the My Projects page for a combined job estimate with cost totals. Everything is stored only in your browser, never uploaded — see the Privacy Policy for details.
Estimates only. Coverage rates vary by paint brand, surface texture, and application method — check the product label for the exact rate.