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Paint Calculator

Calculate gallons of paint and primer for walls, ceilings and trim by coat.

What are you painting?
Measurements
Measure by
ft
ft
ft
Openings to deduct

Doors and windows come off at their actual area, unlike drywall estimating where small openings stay in.

sq ft

A 3'0" × 7'0" door is 21 square feet.

sq ft

A 3' × 5' window is 15 square feet.

Coverage and coats
Pricing
$

Paint to buy

3gallons

2.09 gallons is the exact requirement — 365 sq ft × 2 coats ÷ 350 sq ft per gallon.
Paintable area416 sq ft gross less 51 sq ft of openings
365 sq ft
Total cost3 gal at $48
$144
Area covered per coat350 sq ft per gallon on this surface
365 sq ft
Leftover after the jobKeep it sealed and labeled for touch-ups
0.91 gal

Order one extra quart, not one extra gallon

2.09 gallons rounds up to 3, which leaves 0.91 gallons over. If you go back for more later, the new batch will not match exactly — have the store box your cans together now, or buy the extra quart from the same batch.
Surface by surface
SurfaceDimensionsArea
Wall — length side14.0 × 8.0 ft112.0 sq ft
Wall — length side (opposite)14.0 × 8.0 ft112.0 sq ft
Wall — width side12.0 × 8.0 ft96.0 sq ft
Wall — width side (opposite)12.0 × 8.0 ft96.0 sq ft
Doors deducted1 × 21.0 sq ft−21.0 sq ft
Windows deducted2 × 15.0 sq ft−30.0 sq ft
Paintable area2 coats at 350 sq ft/gal365.0 sq ft
Materials and cost
ItemExact needBuyCost
Finish paint, 2 coats2.09 gal3 gallons$144
Coverage assumed350 sq ft/galSmooth, previously painted—
Total730 sq ft of coating$144

The coverage printed on a can assumes a smooth, sealed, similarly colored surface applied by spray. Rolling over texture, or covering a dark color with a light one, routinely lands closer to 250 square feet per gallon in practice. Deep bases and saturated colors cover worse still, because the tint displaces the solids that do the hiding — plan on three coats for a true red or a deep blue regardless of what this estimate says.

What this assumes

  • Standard coverage is 350 square feet per gallon on smooth, previously painted surfaces.
  • Textured, porous or bare surfaces reduce coverage to roughly 250 square feet per gallon.
  • Doors and windows are deducted at actual area.

Understanding the result

Coverage claims are optimistic

The 350–400 square feet per gallon printed on a can assumes a smooth, sealed, similarly colored surface applied by spray. Rolling over texture, or covering a dark color, routinely lands closer to 250 square feet per gallon.

When primer actually pays

Primer is worth the extra coat over bare drywall, over patches, over glossy surfaces, and when making a large color change. Over sound, similar-colored paint, a second coat of finish paint does more good than a coat of primer.

Ceilings use more paint than walls

Textured ceilings absorb more paint than smooth walls — often 250 square feet per gallon instead of 350. Popcorn ceilings can drop to 200 square feet per gallon. Budget an extra gallon for a textured ceiling in a medium-sized room.

Exterior paint has different coverage

Exterior paint on rough siding covers 150 to 250 square feet per gallon depending on texture. Stucco and rough-sawn cedar are at the low end. Smooth lap siding approaches 300 square feet per gallon. Exterior jobs almost always need two coats on bare wood.

Common questions

How much paint for a 12x12 room?
A 12×12 room with 8-foot ceilings has 384 square feet of wall area. At 350 square feet per gallon with two coats, you need 2.2 gallons — buy 3 gallons. Add 1 gallon for the 144-square-foot ceiling. Total: 4 gallons for walls and ceiling with two coats.
How many gallons of paint for 1000 square feet?
One coat on 1,000 square feet of smooth, previously painted surface needs roughly 3 gallons at 350 square feet per gallon. Two coats need 6 gallons. On bare drywall or textured surfaces at 250 square feet per gallon, two coats need 8 gallons.
How much paint for a 10x10 room?
A 10×10 room with 8-foot ceilings has 320 square feet of walls. Two coats at 350 square feet per gallon needs 1.8 gallons — buy 2 gallons. The 100-square-foot ceiling adds another half gallon. One gallon of primer on bare drywall before painting.
How many square feet does a gallon of paint cover?
A gallon covers 350 to 400 square feet on smooth, sealed surfaces in one coat. Textured, porous, or bare surfaces cover 250 to 300 square feet per gallon. Dark colors over light colors may need a third coat, effectively cutting coverage to 230 square feet per gallon.
How much paint for exterior of house?
A 1,500 square foot ranch with 8-foot walls has roughly 1,200 square feet of paintable siding after deducting windows and doors. Two coats at 250 square feet per gallon on wood siding needs 10 gallons. Stucco or rough texture may need 12 to 14 gallons.
Do I need primer before painting?
Yes on bare drywall, patched walls, glossy surfaces, and when changing from dark to light colors. No on sound, clean, same-color repaints. One gallon of primer covers about 300 square feet. Primer costs $25 to $40 per gallon — less than topcoat.
How much paint for a ceiling?
A 12×12 ceiling is 144 square feet. Flat ceiling paint covers 350 to 400 square feet per gallon, so one gallon covers the ceiling with one coat. Textured popcorn ceilings may need 1.5 gallons for full coverage. Use flat finish to hide imperfections.
How many coats of paint on new drywall?
New drywall needs one coat of primer plus two coats of finish paint. The primer seals the paper and compound; the first finish coat provides color; the second provides uniform sheen and coverage. Skipping primer on new drywall causes flashing at seams.
How much does a gallon of paint cost?
Interior latex paint runs $30 to $60 per gallon for quality brands. Exterior paint runs $40 to $70. Primer runs $25 to $40. A 12×12 room with primer and two coats of wall paint costs $100 to $180 in paint alone.
How much paint for trim and doors?
A standard interior door (both sides) is about 40 square feet. One gallon of trim paint covers 6 to 8 doors with two coats. Baseboard and trim in a 12×12 room add roughly 80 linear feet at 4 inches tall — about 27 square feet, less than a quart.

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