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Paint Calculator

Add your rooms for the exact paint needed — in gallons or litres — plus the primer, tape, rollers and drop cloths you'll actually need.

Show paint in
Input
Waste allowance10%
Coverage per gallonsq ft

These assumptions are yours to adjust — we never pad quantities.

You'll need
2.25 gal
  • Buy 2 × 1 gal + 1 × 1 qt cans of interior paint
  • 1.25 gal of primer — 1 × 1 gal + 1 × 1 qt cans

Materials list

Painter's tape1 roll
≈ 126 ft of edges · 180 ft per roll
Roller covers2 covers
About one cover per coat.
Tray liners2 liners
One per coat keeps cleanup quick.
Drop cloths2 cloths
Covers ≈ 144 sq ft of floor
Paintable caulk2 tubesoptional
For sealing trim gaps before painting.

Tools you'll want

Buy-once items — skip any you already own.

Angled sash brush
For cutting in edges & trim.
Roller frame + tray
Extension poleoptional

Where to buy (optional)

Happy with your list? Tap any item below to open it at a retailer. These are affiliate links that support the site at no extra cost.

Estimates only — verify quantities before buying.

What actually affects how much paint you need

Square footage is only the starting point. Wall texture changes how much paint gets absorbed — smooth, previously painted drywall takes less than bare drywall, brick, or stucco, which can soak up an extra coat. Color change matters just as much: going from a pale wall to a saturated or dark color (or the reverse) usually needs two full coats and sometimes a tinted primer, while touching up a similar shade can often get by with one. Sheen plays a small role too — flat and eggshell finishes spread slightly further per gallon than semi-gloss or high-gloss, which carry less pigment volume. This calculator starts from a standard 350–400 sq ft per gallon coverage rate and lets you adjust coats, primer and waste allowance so the number matches your walls, not a generic room.

How to calculate how much paint you need

Paint is estimated from the paintable area — the wall surface left after you remove doors and windows. For each room the calculator works out:

paintable area = (room perimeter × wall height) − openings
gallons = (paintable area × coats × (1 + waste%)) ÷ coverage

Add as many rooms as you like and the areas are summed. A standard interior door is treated as 21 sq ft and a window as 15 sq ft. One gallon covers about 350–400 sq ft per coat, so we use 350 by default and round up to the nearest quart — never a padded whole gallon.

Common mistakes

  • Forgetting the second coat — most colours need two for even coverage.
  • Skipping primer on bare drywall or big colour changes.
  • Buying paint for one room when the whole project needs more — add every room above.

Frequently asked questions

How much paint do I need for a 12x12 room?+

A 12 × 12 ft room with 8 ft walls has about 384 sq ft of wall area. After subtracting a standard door and window (≈348 sq ft) and adding 10% for waste, two coats need about 2¼ gallons of paint — that is, 2 gallons plus a quart. Add about 1 gallon of primer if the walls are bare, patched, or changing colour.

How much does a gallon of paint cover?+

One gallon of interior latex paint typically covers 350 to 400 sq ft in a single coat on a smooth, primed surface. Rough or porous surfaces cover less, so most projects plan on the lower end and apply two coats.

Can I calculate paint for a whole house or multiple rooms at once?+

Yes — add each room with the “Add another room” button and the calculator totals the wall area across all of them, then gives you the combined paint and materials. You can switch the result between gallons and litres.

How much paint do I need for a ceiling?+

Ceiling paint is based on the floor footprint: length × width. A 12 × 12 ft ceiling is 144 sq ft, so two coats need about 1 gallon. Tick “also paint the ceilings” to add every room’s ceiling automatically.

Is one coat of paint enough?+

One coat can work when repainting a similar colour over a primed, sealed surface. For colour changes, bare drywall, or deep colours, plan on two coats for even coverage. Set the number of coats and the estimate updates instantly.

What is a waste allowance and what should I use?+

A waste allowance is a little extra paint added to cover spills, touch-ups, uneven or textured surfaces, and a margin so you don’t run short mid-wall. 10% is a sensible default; bump it to 15–20% for textured walls, lots of cutting-in, or deep colours.

Do I need primer?+

Use primer on new drywall, patched areas, stains, glossy finishes, or big colour changes. When repainting a similar colour over a sound wall, a paint-and-primer product in two coats is usually enough.

Related calculators

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Reviewed by the RenoSheets team for calculation accuracy. Method: standard coverage rates (350–400 sq ft/gal) with a user-adjustable waste allowance, summed across rooms. Last updated 2026-05-26. Estimates only — verify before purchasing.