Paint Calculator

How much paint do I need for a 12 by 12 room?

A 12 by 12 bedroom with 8 ft ceilings carries 384 sq ft of wall. One door at 20 sq ft and one window at 15 sq ft come off that figure, which leaves 349 sq ft of paintable wall and 1.99 gallons for two coats at 350 sq ft per gallon, so two 1-gallon cans finish the room.

How to calculate paint needed anywhere else is the same four steps, perimeter times height, minus the openings, times the coats, divided by the coverage. Baseboards, casings and the door faces sit outside that 349 sq ft, since the openings get subtracted and nothing adds them back. Trim takes its own quart of enamel.

How many square feet does a gallon of paint cover?

Manufacturers print 350 to 400 sq ft per gallon on the back of the can, a rating measured over primed wall, meaning a surface sealed with a base coat. The calculator opens at the low end of that band.

Bare joint compound, unprimed wood and heavy roll-on texture drop the real figure toward 250 sq ft per gallon. Used as a paint coverage calculator, the form takes whatever number the can in hand claims. The metric selector reads that same rating in m² per litre, where 350 sq ft per gallon becomes 8.6.

Paint needed by room size

Every row below assumes 8 ft walls, one door, one window and two coats at 350 sq ft per gallon, with the ceiling toggle off. The formula assumes a rectangular room, so an L-shape goes in as two rectangles.

Why two coats is the norm on bare drywall

Fresh drywall and patched joint compound absorb the first coat unevenly, so the filled spots come out duller than the paper facing around them. Only the second pass levels that sheen out, which is the reason the coats field opens at 2. One coat holds up on a same-colour, same-sheen refresh over sound paint.

How to calculate paint for exterior walls

Outside, the same four steps apply while the coverage number falls, since siding, stucco and bare masonry drink far more than finished drywall. A gallon that stretches to 350 sq ft indoors covers 250 to 300 sq ft on lap siding and less again on rough stucco or brick. As an exterior paint calculator, the form takes the footprint as length and width, the height from grade to the eave and a lower coverage.

A 40 by 30 house with 9 ft walls, two doors and twelve windows at 275 sq ft per gallon needs 7.56 gallons for two coats, one 5-gallon pail plus three 1-gallon cans. The same house left on the interior default of 350 sq ft per gallon comes out at 5.94 gallons. Running an interior paint calculator number on siding therefore under-buys by about 1.6 gallons, two 1-gallon cans short of the job.

Which cans to buy once the gallons are known

In gallons, wall paint is stocked mainly in 1-gallon cans and 5-gallon pails, so a how much paint do I need calculator that stops at 4.19 gallons leaves the decision half made. The panel plans in those two formats and rounds up to whole cans. Any requirement above 4 gallons would take five singles, so the list swaps them for one 5-gallon pail.

The leftover line underneath reports the overshoot. The 12 by 12 bedroom lands under 1 fluid ounce clear of its two cans, too little to touch up a scuff later, while the 24 by 24 room ends up with 0.81 gallon of the pail unused.

How many litres of paint do I need?

Metric mode takes the room in metres and gives the answer in litres. A 5 by 4 m bedroom with 2.5 m walls carries 45 m² of wall. One door and two windows take 4.6 m² off that. Two coats over the remaining 40.4 m² make 80.7 m² of painted surface, so 8.6 m² per litre works out at 9.38 litres.

The same can logic runs on metric tins, which come in 5 L, 2.5 L and 1 L. Those 9.38 litres return one 5 L tin, one 2.5 L tin and two 1 L tins, so 9.5 L gets bought against 9.38 L needed. European tins often state 10 to 12 m² per litre, a figure measured on smooth, already painted wall, so the number printed on the tin in hand belongs in the coverage field ahead of the 8.6 default.