gizmobench

Paint Calculator

Type each wall as a width and a height, take the doors and windows off as real openings with a count, pick the coats, and read the litres or gallons and the whole tins to buy together. The spread rate is a field rather than a fixed assumption: it opens on 350 square feet per US gallon, or 11 square metres per litre, which is the figure commonly printed on interior emulsion tins, and the tin in your hand overrides it in one keystroke.

Paint needed0galType a wall width and height to start, in feet.
Wall area
not yet
Openings
0 sq ft
Coats
Spread rate, editable
Per
sq ft per gallon
Tin size
Units
Leading with

Measure each wall along the floor and up to the ceiling and type the two numbers. A ceiling is one more surface: its length and its width. The spread rate opens on 350 sq ft per gallon, which is the figure commonly printed on interior emulsion tins, and the one on your tin is the one that counts, so change it.

Walls and ceilings

Each surface is a width and a height, in feet.

  • not yet

Doors and windows

Anything you are not painting comes off here. Add one line per size and say how many of it there are.

Worked examples

Each one is run through the same two functions as your own numbers. Load one to see it in the fields.

  • A 12 by 14 ft room8 ft ceilings, one door, two windows, 2 coats at 350
    371 sq ft net · 2.12 gal · buy 3 × 1 gal
  • A ceiling on its own12 by 14 ft, 1 coat at 350
    168 sq ft net · 0.48 gal · buy 1 × 1 gal
  • A 5 by 4 m room2.4 m high, one door, two windows, 2 coats at 11
    38.52 m² net · 7 L · buy 3 × 2.5 L
Quantity, not chemistry. Exact arithmetic on the area, coats and spread rate you give, with your openings subtracted. The spread rate on your tin is the one that counts. It cannot know how porous the wall is or how much colour change you are covering. There is no product list here and nothing to buy: the page gives you an area, a volume and a tin count, and stops.

Common questions

How much wall does a gallon of paint cover?
The spread rate field opens on 350 square feet per US gallon, or 11 square metres per litre, because that is the figure commonly printed on interior emulsion tins. It is a starting value and nothing more. Your tin states its own rate for that paint on that kind of surface, and it is the one that counts, so type it over the default. A different rate changes the answer in exact proportion: halve the rate and the paint doubles.
Should I subtract doors and windows?
Yes, and this page takes them off as real openings rather than as a flat percentage. Add one line per size, say how many of that size there are, and the area comes off the total. There are one-click lines for a 32 by 80 inch door and a 3 by 4 foot window in feet, and a 0.81 by 2.03 metre door and a 0.9 by 1.2 metre window in metres, all of them editable. If the openings ever add up to more than the walls, the page says so instead of returning a nonsense figure.
How many coats do I need?
The page multiplies by the number of coats you choose and does not decide it for you, because the answer depends on things it cannot see: how porous or freshly plastered the wall is, how big the colour change is, and how well the paint covers. Set 1, 2 or 3 and the working updates. What the page can tell you exactly is what each choice takes: three coats is three times the paint of one, on the same wall at the same spread rate.
Why does the answer round up to whole tins?
Because a tin is indivisible at the shop. The volume is shown to two decimal places, or to three significant figures when it is under one, and the tin count is that volume divided by the tin size you picked, rounded up. Two gallons exactly is two one-gallon tins, not three; a hair over two is three. Tin sizes offered are one quart, one gallon and five gallons in feet, and 1, 2.5, 5 and 10 litres in metres.
Can I mix feet and metres?
The page works in one system at a time. The units switch reads every measurement as feet or as metres, and it resets the spread rate to that system's default and the tin to that system's usual size, so a metric tin and an imperial room never get multiplied together by accident. The paint-needed line gives both, the litres beside the gallons, converted with the exact 3.785411784 litres per US gallon, and the copied summary carries both as well.
Is anything uploaded?
No. Every measurement is read and multiplied in your browser and nothing is sent anywhere. Your walls, openings, coats, spread rate and tin size are remembered in your own browser storage so the page reopens where you left it, and clearing your browser data clears them.

Exact arithmetic on the area, coats and spread rate you give, with your openings subtracted. The spread rate on your tin is the one that counts. It cannot know how porous the wall is or how much colour change you are covering.