Solve backwards
How much wall will my primer cover?
- 5 galThe example worked below
- Paint Primer CalculatorEvery figure is its own
You have
How much primer?
That is 5 gal(18.9 L). Worked by the Paint Primer Calculator at the settings below.
The settings it uses
- Spread rate
- 200 ft²/gal
What it will do
1,000 sq ft of wall
92.9 m²
One room. Enough for the walls of a room about 31 × 31 ft with 8 ft walls.
Or several. About 2 rooms of the size the Paint Primer Calculator opens on: the walls of a room about 13.4 × 13.4 ft with 8 ft walls.
Check it forwards
- Wall Area
- 1,000 sq ft
- It asks for
- 5 gal
- You have
- 5 gal
The Paint Primer Calculator asks for 5 gal at that size, and 5.5 gal one step larger.
If you had more, or less
Around your amount
Each worked by the Paint Primer Calculator at the same settings.
Half
2.5 gal
500 sq ft
the walls of a room about 15.6 × 15.6 ft with 8 ft walls
Yours
5 gal
1,000 sq ft
the walls of a room about 31 × 31 ft with 8 ft walls
Half as much again
7.5 gal
1,500 sq ft
the walls of a room about 47 × 47 ft with 8 ft walls
Double
10 gal
2,000 sq ft
the walls of a room about 63 × 63 ft with 8 ft walls
Common amounts
What each amount of primer covers
The sizes it is usually sold in, each worked by the Paint Primer Calculator at the settings above.
| You have | It covers | As one room | Average rooms |
|---|---|---|---|
| 1 gal(3.8 L) | 200 sq ft(18.6 m²) | the walls of a room about 6.3 × 6.3 ft with 8 ft walls | under 1 |
| 2 gal(7.6 L) | 400 sq ft(37.2 m²) | the walls of a room about 12.5 × 12.5 ft with 8 ft walls | under 1 |
| 5 gal(18.9 L) | 1,000 sq ft(92.9 m²) | the walls of a room about 31 × 31 ft with 8 ft walls | 2 |
Primer spreads by what it goes onto
The calculator opens at 200 square feet per US gallon, about 19 m² per 3.8 litres — a general-purpose figure for bare plaster, new board and raw timber, which drink primer. A sealed or previously painted surface takes far less, and a primer tin often rates it at 300 to 400 square feet per gallon. Put your tin's figure for your surface into the calculator.
The half gallon is a step, not a tin
The primer calculator rounds up to the next half US gallon, so the area here is the largest one whose rounded requirement still fits in what you have. A half gallon is two quarts in practice rather than a size on the shelf, and in litres the step is still a converted US half gallon rather than a metric tin.
One coat, and the openings still in
The answer is one coat over every square foot of the area — there is no coat count in the calculator, and doors and windows are not taken off unless you took them off the area yourself. Knots, water stains or a strong colour to cover can want two coats of primer, which halves the room this reaches.
How the answer is worked
Nothing here is a second formula. The Paint Primer Calculator runs forwards — a size in, a quantity out — and this page grows its own starting room in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.
Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.
Paint Primer Calculator
runs it forwardsEstimate how many gallons or litres of primer you need before painting, using primer's lower coverage rate.
Work out what to buy insteadSolve backwards
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Solve backwards
Start from what is already in the yard
Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.
The calculator's own figures
Nothing is estimated twice: the page runs the same calculator you would order with.
The largest size that fits
Where a calculator rounds up to whole containers, the answer stops before the next one.
Both unit systems
Gallons and litres, square feet and square metres, side by side.
Frequently asked questions
- How much wall does 5 gal of primer cover?
- At the Paint Primer Calculator's own settings, 1,000 sq ft (92.9 m²) — the walls of a room about 31 × 31 ft with 8 ft walls. That is about 2 rooms of the size the calculator opens on: the walls of a room about 13.4 × 13.4 ft with 8 ft walls. Every figure follows the settings, which you can change in the calculator.
- How much wall does 10 L of primer cover?
- At the Paint Primer Calculator's own settings, 46.5 m² (500 sq ft) — the walls of a room about 4.8 × 4.8 m with 2.4 m walls. That is about 1 room of the size the calculator opens on: the walls of a room about 4.2 × 4.2 m with 2.4 m walls. Every figure follows the settings, which you can change in the calculator.
- How many square feet does a gallon of primer cover?
- On bare, porous surfaces about 200 square feet per US gallon, roughly 19 m² per 3.8 litres, which is the calculator's opening figure. On a sealed or painted surface many primers rate 300 to 400 square feet per gallon. It depends on the product and the surface more than on the brand.
- Why does primer cover less than paint?
- Because it is formulated to seal and bond rather than to spread thin. A primer's job is to soak into the surface and even out its suction so the paint over it dries evenly — which is exactly why it goes a shorter way than the topcoat's 350 to 400 square feet per gallon.
- Do I need to prime new plaster or a painted wall?
- Fresh plaster usually wants a thinned mist coat rather than a primer, and a sound, previously painted wall in a similar colour often needs none. Stain-blocking, bonding and masonry primers differ in spread rate by more than primer differs from paint, so choose it for what it must do and enter its own rate.