Paint Calculator - How Many Gallons for Walls and Ceilings

The wall is half done and the can is empty

Running out of paint mid-project means a second trip to the store, a potential color mismatch between batches, and wasted time. This calculator takes four inputs - area, paint type, number of coats and safety margin - and returns the exact number of gallons to buy. Add a price per gallon and it shows total material cost too.

A 400 sq ft room (typical 12x14 ft with 8 ft ceilings) with 2 coats of latex paint and a 10% margin needs about 2.3 gallons - so you buy 3 gallons. At $35/gallon that is $105 in paint. The leftover covers touch-ups for years.

How to use - step by step

Area to paint - measure each wall (height x width) and add them up. Subtract windows and doors for precision. A 12x14 ft room with 8 ft ceilings has about 416 sq ft of wall.
Paint type - latex is the most popular and easiest to clean. Oil-based covers more per gallon but needs mineral spirits. Acrylic is more durable for high-traffic areas.
Number of coats - 2 coats is standard. Use 3 when changing from dark to light or covering stains.
Safety margin - 10% for smooth drywall. 15-20% for textured, brick or rough surfaces.
Price per gallon (optional) - enter to get total cost and cost per square foot.
Read results - gallons needed, coverage comparison across 5 paint types, and cost breakdown.

Coverage rates by paint type

Paint type	Coverage (sq ft/gal)	Best for	Cleanup
Latex	350-400	Walls, ceilings	Water
Acrylic	300-350	High-traffic, exteriors	Water
Emulsion	350-400	Budget projects	Water
Oil-based	400-450	Trim, doors, cabinets	Mineral spirits
Chalk	350-400	Furniture, decorative	Water

The problem - and how the calculator solves it

The problem

You guess how much paint you need. You buy 2 gallons. Halfway through the second coat the roller starts dragging. The store is closed. Tomorrow you get a new can from a different batch - and the color is slightly off. Every painter has this story.

The solution

Measure the area. Enter paint type and coats. Add a margin for texture and waste. Buy the exact number of gallons - rounded up. The leftover is your touch-up reserve. One trip. One batch. One consistent color on every wall.

How much does surface texture affect paint usage?

Surface type	Extra paint needed	Recommended margin
Smooth drywall (painted)	0%	5-10%
New drywall (primed)	+5-10%	10-15%
Light texture (orange peel)	+10-15%	15%
Heavy texture (knockdown)	+15-25%	20%
Brick or stucco	+20-35%	20%
Bare wood (unprimed)	+25-40%	20%

Practical examples

Example 1: Small bedroom - 300 sq ft walls, latex, 2 coats, 10% margin
Need: 1.8 gal - buy 2 gallons. At $35/gal = $70

Example 2: Living room - 600 sq ft walls, acrylic, 2 coats, 10% margin
Need: 4.1 gal - buy 5 gallons. At $45/gal = $225

Example 3: Entire house interior - 2,400 sq ft, latex, 2 coats, 15% margin
Need: 14.7 gal - buy 15 gallons (3 x 5-gal bucket). At $30/gal = $450

Example 4: Kitchen cabinets - 80 sq ft, oil-based, 3 coats, 15% margin
Need: 0.6 gal - buy 1 gallon. At $55/gal = $55

Example 5: Color change (dark to light) - 500 sq ft, latex, 3 coats, 10% margin
Need: 4.4 gal - buy 5 gallons. At $40/gal = $200

FAQ - Frequently asked questions

How much does one gallon of paint cover?

One gallon covers 350-400 sq ft on smooth, previously painted drywall. That is roughly the walls of a 10x12 ft room with 8 ft ceilings (one coat). Textured surfaces, bare wood or brick can reduce coverage by 20-40%.

Do I need a primer coat?

Use primer on: bare drywall, bare wood, stains you want to block, and when going from very dark to very light. Modern paint-and-primer combos reduce the need, but a dedicated primer still gives better adhesion and color accuracy. Primer is a separate purchase - this calculator covers topcoat only.

Is expensive paint worth it?

Generally yes. Premium paints ($50-80/gal) have higher pigment concentration, which means better coverage in fewer coats, better washability, and longer life. A $70 gallon that covers in one coat can be cheaper than two coats of $30 paint - and the result looks better. The cost difference over a whole room is often just $50-100.

How do I calculate wall area for a room?

Measure the perimeter (sum of all wall lengths) and multiply by ceiling height. Example: a 12x14 ft room has a perimeter of 52 ft. At 8 ft ceilings: 52 x 8 = 416 sq ft. Subtract windows (~15 sq ft each) and doors (~20 sq ft each) for a more precise number.

Roller vs brush vs sprayer - does it affect paint usage?

Yes. A roller uses the least paint and gives even coverage. A brush uses 10-15% more due to thicker application but is needed for edges and trim. A sprayer uses 20-30% more because of overspray - but covers large areas much faster. For whole rooms, roll the walls and brush the edges.

Should I buy one big bucket or several small cans?

If you need 4+ gallons of the same color, buy a 5-gallon bucket. It is 15-25% cheaper per gallon than individual cans, and - critically - all the paint comes from the same batch so there is zero color variation. For smaller jobs, single gallons are fine. Always buy from the same batch number.

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