TradesHow this works
The tool takes your paintable area, the number of coats, and the surface coverage rate to work out gallons, then decides whether you need primer. Priming is not busywork: a bare or stained surface, or a drastic color change, either bleeds through or eats an extra finish coat if you skip it. On a sound painted wall going to a close color, you can skip primer and save a can.
Coverage is manufacturer-dependent, so treat the number as typical and match it to your paint's spec sheet. Always buy a little extra for cutting in and touch-ups.
Common questions
How many gallons of paint do I need?
Take the paintable area, multiply by the number of coats, and divide by the coverage rate, then round up. An average wall covers about 350 square feet per gallon; smooth sealed surfaces cover more, rough or porous ones less. This tool does the math and adds primer when your surface needs it.
Do I need primer?
Prime when the surface is bare (new drywall or wood), when it is stained or marked, or when you are making a drastic color change. On a sound, previously painted wall going to a similar color, two coats of finish without primer is usually enough. The tool makes that call from your inputs.
One coat or two?
Two coats is the standard for an even, durable finish. A same-color refresh on a wall in good shape can be a single coat. Deep or drastic colors sometimes need a third coat, which is where a tinted primer earns its keep.
Why does surface texture matter?
Rough and porous surfaces drink paint. A textured wall or bare masonry can drop coverage from 400 down to 300 square feet per gallon, which on a large room is a full extra gallon. Match the surface setting to what you are actually painting.
Sources: Typical interior latex coverage ~350-400 sq ft/gal (manufacturer-dependent). Engine version 1.0.0. Risk tier 1.