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Primer chart
Put your area, coverage per gallon and waste allowance in: 400 sq ft at 10% waste needs 1.47 gallons exact, order 2.
★ CONSTRUCTION · PRIMER · COVERAGE CHART
Primer Chart: 2 Gallons for 400 Sq Ft at 10% Waste
On the defaults — 400 square feet at 10% waste with 300 square feet per gallon coverage — you need 440.00 square feet of primer, 1.47 gallons exact, so order 2 gallons. This is the PRIMER version — area times waste divided by coverage, with a lookup table for every common area — the paint-chart page is the PAINT version — the same divide-and-round-up model counted in topcoat gallons; the drywall-chart page is the SHEET version — the same model counted in sheets; and the caulk-chart page is the TUBE version — the same model counted in tubes.
What does 1.47 gallons, order 2, mean?
It means that 400 square feet of surface, with a 10% waste allowance, need 440.00 square feet of primer, and at 300 square feet per gallon that is 1.47 gallons — one full gallon plus nearly half of a second — and because primer is sold by the gallon, you order 2. The rounding is the whole story in miniature: a partial gallon cannot be bought in the quantity needed, so any fraction, however small, becomes a whole gallon. The part people get wrong is rounding to the nearest gallon instead of up: 1.47 rounded to the nearest is 1, and 1 gallon covers only 300 square feet, leaving 140.00 square feet unprimed. The other part people get wrong is the exact fit: 440 square feet of coverage need exactly 1.00 gallon, and order exactly 1, because the rounding is up to the next whole gallon, not up plus one — an exact fit needs no spare gallon from the rounding, though a spare for touch-ups is a separate decision.
Three things to check before you trust the number
Is 300 square feet per gallon right for your primer? Three hundred square feet per gallon is a typical primer figure used on this page, and published primer coverage varies with product and surface, roughly from 200 to 400 square feet per gallon. If your primer is thinner or your surface thirstier, one gallon covers fewer feet: the 350-square-feet branch needs 1.26 gallons exact, order 2, for the same 400 square feet, so the order is unchanged there — but on a larger job the coverage figure decides whole gallons. Enter your own figure if your product differs, rather than trusting the default for a thirsty surface.
Did you measure every surface? The area entered here must be the total of all surfaces, not the largest single wall: a room with four 10-by-8-foot walls has 320 square feet of wall, before the ceiling is added. The 200-square-foot branch needs 0.73 gallons, order 1, against the 1.47-gallon headline, so missing one wall understates the order by a whole gallon on a bigger job. Measure every wall and ceiling, subtract nothing for small openings unless your primer maker says to, and add the surfaces before dividing.
Are you counting waste, or a second coat? This page adds 10% for waste — roller absorption, spills and touch-ups — and that is not a second coat. A second coat doubles the area first: 400 square feet twice-coated is 800 square feet before waste, which is 880.00 square feet with waste and 2.93 gallons, order 3. Treating a second coat as waste, or waste as a second coat, misstates the order by a whole gallon either way, so decide the coats first and let the waste percentage stay at waste.
Worked example
On the defaults: 400 square feet, 300 square feet per gallon, 10% waste.
- Needed area: 400 × 1.10 is 440.00 square feet.
- Exact gallons: 440.00 ÷ 300 is 1.47 gallons.
- Order: 1.47 rounded up is 2 gallons — the 0.47 is nearly half a gallon that must be bought whole.
- Check: 2 gallons cover 600 square feet, which is more than the 440.00 needed; 1 gallon covers only 300, which is not enough.
And the other way: the area behind 1.47 gallons is 400 square feet, the coverage behind 1.47 gallons is 300 square feet per gallon, and the waste behind 1.47 gallons is 10%. A job at 440 square feet per gallon orders exactly 1 gallon, and the 3,000-square-foot lookup row lands exactly on 11.00 gallons, order 11.
Every branch, checked
- 200 square feet, 300 square feet per gallon, 10% waste: 200 square feet, 300 square feet per gallon, 10% waste: 0.73 gallons exact — order 1 gallons.
- 800 square feet, 300 square feet per gallon, 10% waste: 800 square feet, 300 square feet per gallon, 10% waste: 2.93 gallons exact — order 3 gallons.
- 400 square feet, 350 square feet per gallon, 10% waste: 400 square feet, 350 square feet per gallon, 10% waste: 1.26 gallons exact — order 2 gallons.
- 400 square feet, 300 square feet per gallon, 20% waste: 400 square feet, 300 square feet per gallon, 20% waste: 1.60 gallons exact — order 2 gallons.
The reverses, worked backwards
- Area behind 1.47 gallons: 400 sq ft — at 400 sq ft the figures are 1.47 gallons exact — order 2 gallons.; at the lower neighbor the figures are 1.28 gallons exact — order 2 gallons.; at the upper neighbor the figures are 1.65 gallons exact — order 2 gallons..
- Coverage behind 1.47 gallons: 300 sq ft per gallon — at 300 sq ft per gallon the figures are 1.47 gallons exact — order 2 gallons.; at the lower neighbor the figures are 1.76 gallons exact — order 2 gallons.; at the upper neighbor the figures are 1.26 gallons exact — order 2 gallons..
- Waste behind 1.47 gallons: 10% waste — at 10% waste the figures are 1.47 gallons exact — order 2 gallons.; at the lower neighbor the figures are 1.40 gallons exact — order 2 gallons.; at the upper neighbor the figures are 1.53 gallons exact — order 2 gallons..
What the defaults assume
The defaults are 400 square feet, 300 square feet per gallon and 10% waste, so the headline is one coat of a typical primer over a small room. The model is a multiplication, a division and a ceiling: needed area is area times one plus the waste percentage, exact gallons are needed area divided by coverage per gallon, and the order rounds exact gallons up to the next whole gallon, with a 1e-12 epsilon so an exact whole number orders exactly that many. The area reverse is checked at 50 square feet either side, because 50 square feet at 10% waste is 55 square feet, about 0.18 gallons; the coverage reverse is checked at 50 square feet either side, because 440.00 over 250 is 1.76 gallons and over 350 is 1.26; the waste reverse is checked at 5% either side, because 5% of 400 is 20 square feet, about 0.07 gallons. The model does not include second coats, primer type differences beyond the coverage figure, surface porosity beyond the waste allowance, or tools — count those separately.
Lookup table: gallons by area
Each row already includes the 10% waste allowance: needed area is the area times 1.10, exact gallons are needed area divided by 300 square feet per gallon, and the order column rounds up. A row that lands exactly on a whole number orders exactly that many — no extra gallon is added for an exact fit. For a different primer, enter your own coverage in the calculator above: a lower-coverage primer covers fewer feet per gallon, so the order rises.
| Area | Coverage per gallon | Needed area | Exact gallons | Order |
|---|---|---|---|---|
| 100 sq ft | 300 sq ft per gallon | 110.00 sq ft | 0.37 | 1 gallons |
| 200 sq ft | 300 sq ft per gallon | 220.00 sq ft | 0.73 | 1 gallons |
| 300 sq ft | 300 sq ft per gallon | 330.00 sq ft | 1.10 | 2 gallons |
| 400 sq ft | 300 sq ft per gallon | 440.00 sq ft | 1.47 | 2 gallons |
| 500 sq ft | 300 sq ft per gallon | 550.00 sq ft | 1.83 | 2 gallons |
| 600 sq ft | 300 sq ft per gallon | 660.00 sq ft | 2.20 | 3 gallons |
| 800 sq ft | 300 sq ft per gallon | 880.00 sq ft | 2.93 | 3 gallons |
| 1,000 sq ft | 300 sq ft per gallon | 1,100.00 sq ft | 3.67 | 4 gallons |
| 1,200 sq ft | 300 sq ft per gallon | 1,320.00 sq ft | 4.40 | 5 gallons |
| 1,500 sq ft | 300 sq ft per gallon | 1,650.00 sq ft | 5.50 | 6 gallons |
| 1,800 sq ft | 300 sq ft per gallon | 1,980.00 sq ft | 6.60 | 7 gallons |
| 2,000 sq ft | 300 sq ft per gallon | 2,200.00 sq ft | 7.33 | 8 gallons |
| 2,400 sq ft | 300 sq ft per gallon | 2,640.00 sq ft | 8.80 | 9 gallons |
| 3,000 sq ft | 300 sq ft per gallon | 3,300.00 sq ft | 11.00 | 11 gallons |
| 4,000 sq ft | 300 sq ft per gallon | 4,400.00 sq ft | 14.67 | 15 gallons |
| 5,000 sq ft | 300 sq ft per gallon | 5,500.00 sq ft | 18.33 | 19 gallons |
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Needed area | area × (1 + waste ÷ 100) | 440.00 sq ft — 400 × 1.10. |
| Exact gallons | needed area ÷ coverage per gallon | 1.47 gallons — 440.00 ÷ 300. |
| Order | exact gallons rounded up | 2 gallons — 1.47 rounds up. |
| Area behind a target exact figure | exact gallons × coverage per gallon ÷ (1 + waste ÷ 100) | 400 sq ft — 1.47 × 300 ÷ 1.10. |
| Coverage behind a target exact figure | needed area ÷ exact gallons | 300 sq ft per gallon — 440.00 ÷ 1.47. |
| Gallons covered by the order | order × coverage per gallon | 600 sq ft — 2 × 300, more than the 440.00 needed. |
| Square feet short on one fewer gallon | needed area − (order − 1) × coverage per gallon | 140.00 sq ft — 440.00 − 1 × 300, which is why rounding down fails. |
| 200 square feet, 300 square feet per gallon, 10% waste | same model | 0.73 gallons exact — order 1 gallons. |
| 800 square feet, 300 square feet per gallon, 10% waste | same model | 2.93 gallons exact — order 3 gallons. |
| 400 square feet, 350 square feet per gallon, 10% waste | same model | 1.26 gallons exact — order 2 gallons. |
| 400 square feet, 300 square feet per gallon, 20% waste | same model | 1.60 gallons exact — order 2 gallons. |
| Area behind 1.47 gallons | reverse | 400 sq ft: 1.47 gallons exact — order 2 gallons. |
| Coverage behind 1.47 gallons | reverse | 300 sq ft per gallon: 1.47 gallons exact — order 2 gallons. |
| Waste behind 1.47 gallons | reverse | 10% waste: 1.47 gallons exact — order 2 gallons. |
| 0 square feet | same model | 0.00 gallons exact — order 0 gallons. |
| Negative area | same model | Area — 0 or more. |
| Zero coverage | same model | Coverage — more than 0. |
| 440 square feet per gallon | same model | 1.00 gallons exact — order 1 gallons. |
Who uses this
- A DIYer priming a room — 400 square feet at 10% waste is 2 gallons, with the lookup table covering every other area without re-measuring.
- A painter ordering for a job — the branches show how the order moves with area, coverage and waste, so a thirstier surface is repriced before ordering.
- A homeowner comparing primers — the 350-square-feet branch shows what a higher-coverage primer really saves in gallons, before the job starts.
- An estimator checking a quote — the reverses recover the area, coverage or waste behind any quoted gallon count, which checks a quote without re-measuring the job.
Accuracy & limitations
Figures are the model’s own arithmetic on the numbers you type, computed from unrounded values and displayed rounded HALF_UP to 2dp, with orders rounded up using a 1e-12 epsilon so exact fits are not over-ordered. The main limitation is the coverage figure, not the arithmetic: published primer coverage varies with product and surface, roughly from 200 to 400 square feet per gallon, so check your product and enter your own figure when your surface differs. This page is a calculation tool, not trade advice — follow the primer maker’s instructions for surface preparation and coats.
Cite this calculator
400 square feet at 10% waste with 300 square feet per gallon coverage needs 440.00 square feet, 1.47 gallons exact: order 2 gallons. Source: Bright Side Kit, https://brightoolbox.com/primer-chart/, accessed 29 October 2026.
Frequently asked questions
How many square feet does one gallon of primer cover?
This page uses 300 square feet per gallon, a typical primer figure — but published primer coverage varies with product and surface, roughly from 200 to 400 square feet per gallon. If your primer or surface differs, enter your own coverage figure: the calculator divides by whatever you enter, so the answer stays honest for your product.
Why add 10% waste?
Because rollers absorb primer, spills happen and touch-ups need material: the 10% allowance covers the primer that never lands on the wall as intended. Without it, a job that computes to exactly 1.00 gallon would run dry on the last stretch of wall, and the waste percentage is what keeps the order honest for real application.
Why round up instead of to the nearest gallon?
Because a partial gallon cannot be bought in the quantity needed, and rounding down leaves surface unprimed: 1.47 gallons rounded to the nearest is 1, and 1 gallon covers only 300 of the 440.00 square feet needed. Rounding up guarantees the whole area is covered; the extra fraction is the price of buying whole gallons.
What if the exact figure is already a whole number?
Then you order exactly that many: a job at 440 square feet per gallon needs exactly 1.00 gallon and orders 1, not 2, and the 3,000-square-foot lookup row lands exactly on 11.00 gallons and orders 11. The epsilon in the rounding protects exact fits, so a job that lands on a whole number is not charged an extra gallon for nothing.
Does the waste allowance cover a second coat?
No: waste and coats are different things. Waste is the extra 10% for absorption, spills and touch-ups on one coat; a second coat doubles the area first, so 400 square feet twice-coated is 800 square feet before waste, which is 880.00 square feet with waste and 2.93 gallons, order 3. Decide the coats first, then let waste stay at waste.
Should I buy a spare gallon beyond the order?
That is a separate decision from the order column: the order column is the exact math for the measured area, and a spare covers porous patches, over-rolling and touch-ups. On new drywall or a thirsty surface, one spare is cheap insurance; on a single smooth coat, it is usually unnecessary.