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Joint compound chart calculator
Put your area, coverage per gallon and waste in: 400 square feet at 10% waste with 100 square feet per gallon is 4.40 gallons exact, order 5.
★ CONSTRUCTION · DRYWALL · JOINT COMPOUND CHART
Joint Compound Chart: 5 Gallons for 400 Sq Ft at 10% Waste
On the defaults — 400 square feet at 10% waste with 100 square feet per gallon coverage — you need 440.00 square feet of joint compound coverage, 4.40 gallons exact, so order 5 gallons. This is the JOINT COMPOUND version — area times waste divided by coverage, with a lookup table for every common area and waste level — the tile-adhesive-chart page is the TILE-ADHESIVE version — the same divide-and-round-up model counted in adhesive bags; the thinset-chart page is the THINSET version — the same model counted in thinset bags; the grout-chart page is the GROUT version — the same model counted in grout bags; and the mortar-chart page is the MORTAR version — the same model counted in mortar bags.
What does 4.40 gallons, order 5, mean?
It means that 400 square feet of drywall, once 10% waste is added, needs 440.00 square feet of joint compound coverage, which is 4.40 gallons at 100 square feet a gallon — and since compound is sold by the whole gallon, you order 5. The exact figure and the order figure answer different questions: 4.40 is the arithmetic, 5 is the purchase, and the six-tenths of a gallon of headroom is the waste allowance doing its job rather than an over-order. The part people get wrong is ordering the exact figure rounded down: 4.40 rounded down is 4 gallons, 400.00 square feet of coverage against a 440.00-square-foot need, and the last joints run short. The other part people get wrong is applying the waste percentage to the gallons instead of the area: waste is 10% more surface to cover, not 10% more gallons on top of a rounded order, and the two give different answers once rounding enters.
Three things to check before you trust the number
Is 100 square feet per gallon really your coverage? One hundred square feet is the coverage for the coat system on the bucket, and it is the figure the exact-gallons line turns on: the 80-square-foot-coverage branch totals 5.50 gallons exact against the 4.40 headline, so a 20-square-foot coverage difference is more than a whole gallon on 400 square feet. If you are applying an extra skim coat beyond what the bucket assumes, your real coverage is lower and your real gallon count higher — check the coat count on the product sheet against the coats you are actually applying.
Is 10% waste enough for your joints? Ten percent is the waste allowance, and it is the figure the needed-area line turns on: the 20%-waste branch totals 4.80 gallons exact against the 4.40 headline, so doubling waste adds four-tenths of a gallon here and nearly a gallon on larger jobs. Smooth new drywall at 10% is reasonable; rough joints, patchy repairs, or walls full of corners and angles want 15% or 20%, because every sanded edge and every uneven joint eats compound that a flat-wall figure never sees.
Did you measure every wall? Four hundred square feet is the area, and it is the figure everything else multiplies: the 800-square-foot branch totals 8.80 gallons exact against the 4.40 headline, so a missed wall doubles the order. Measure wall by wall, subtract large openings only if you genuinely will not finish them, and add the corners and angles — small strips that are easy to forget and add up to a gallon on a whole house.
Worked example
On the defaults: 400 square feet, 100 square feet per gallon, 10% waste.
- Needed area: 400 × 1.10 is 440.00 sq ft.
- Exact gallons: 440.00 ÷ 100 is 4.40 gallons.
- Order: 4.40 rounded up is 5 gallons — area times the waste factor, divided by coverage, rounded up to order, with a 1e-12 epsilon guard so a true exact fit is never rounded up by float error.
And the other way: the area behind 4.40 gallons is 400 square feet, the coverage behind 4.40 gallons is 100 square feet per gallon, and the waste behind 4.40 gallons is 10%. With 0% waste the model honestly shows 4.00 gallons exact and an order of 4 — an exact fit where order equals exact and no rounding up is needed, because the need divides evenly by the coverage.
Every branch, checked
- 200 square feet, 100 square feet per gallon, 10% waste: 200 square feet, 100 square feet per gallon, 10% waste: 2.20 gallons exact — order 3 gallons.
- 800 square feet, 100 square feet per gallon, 10% waste: 800 square feet, 100 square feet per gallon, 10% waste: 8.80 gallons exact — order 9 gallons.
- 400 square feet, 80 square feet per gallon, 10% waste: 400 square feet, 80 square feet per gallon, 10% waste: 5.50 gallons exact — order 6 gallons.
- 400 square feet, 100 square feet per gallon, 20% waste: 400 square feet, 100 square feet per gallon, 20% waste: 4.80 gallons exact — order 5 gallons.
The reverses, worked backwards
- Area behind 4.40 gallons: 400 sq ft — at 400 sq ft the figures are 4.40 gallons exact — order 5 gallons.; at the lower neighbor the figures are 3.85 gallons exact — order 4 gallons.; at the upper neighbor the figures are 4.95 gallons exact — order 5 gallons..
- Coverage behind 4.40 gallons: 100 sq ft per gallon — at 100 sq ft per gallon the figures are 4.40 gallons exact — order 5 gallons.; at the lower neighbor the figures are 4.63 gallons exact — order 5 gallons.; at the upper neighbor the figures are 4.19 gallons exact — order 5 gallons..
- Waste behind 4.40 gallons: 10% waste — at 10% waste the figures are 4.40 gallons exact — order 5 gallons.; at the lower neighbor the figures are 4.20 gallons exact — order 5 gallons.; at the upper neighbor the figures are 4.60 gallons exact — order 5 gallons..
What the defaults assume
The defaults are 400 square feet, 100 square feet per gallon and 10% waste, so the headline is one medium room of drywall finishing at a standard coat system with a standard waste allowance. The model is a multiplication, a division and a round-up: the needed area is area times one plus waste over one hundred, the exact gallons are needed area divided by coverage, and the order is exact gallons rounded up to the next whole gallon, guarded by a 1e-12 epsilon so a true exact fit (4.00 gallons at 0% waste) orders exactly 4 rather than 5 on float error. The area reverse is checked at 50 square feet either side, because 50 square feet at 10% waste is 55 square feet, or 0.55 gallons; the coverage reverse is checked at 5 square feet either side; the waste reverse is checked at 5 points either side, because 5 points on 400 square feet is 20 square feet, or 0.20 gallons. The model does not include coat thickness beyond what the coverage figure already assumes, primer, tape, or different products for different coats — price those separately.
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 | 4.40 gallons — 440.00 ÷ 100. |
| Order | exact gallons rounded up (1e-12 epsilon guard) | 5 gallons — 4.40 rounds up to the next whole gallon. |
| Area behind a target exact figure | exact gallons × coverage ÷ (1 + waste ÷ 100) | 400 sq ft — 4.40 × 100 ÷ 1.10. |
| Coverage behind a target exact figure | needed area ÷ exact gallons | 100 sq ft per gallon — 440.00 ÷ 4.40. |
| Waste behind a target exact figure | (exact gallons × coverage ÷ area − 1) × 100 | 10% — (4.40 × 100 ÷ 400 − 1) × 100. |
| Headroom in the order | order − exact gallons | 0.60 gallons — 5 − 4.40, the waste allowance doing its job. |
| 200 square feet, 100 square feet per gallon, 10% waste | same model | 2.20 gallons exact — order 3 gallons. |
| 800 square feet, 100 square feet per gallon, 10% waste | same model | 8.80 gallons exact — order 9 gallons. |
| 400 square feet, 80 square feet per gallon, 10% waste | same model | 5.50 gallons exact — order 6 gallons. |
| 400 square feet, 100 square feet per gallon, 20% waste | same model | 4.80 gallons exact — order 5 gallons. |
| Area behind 4.40 gallons | reverse | 400 sq ft: 4.40 gallons exact — order 5 gallons. |
| Coverage behind 4.40 gallons | reverse | 100 sq ft per gallon: 4.40 gallons exact — order 5 gallons. |
| Waste behind 4.40 gallons | reverse | 10% waste: 4.40 gallons exact — order 5 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. |
| 400 square feet, 0% waste | same model | 4.00 gallons exact — order 4 gallons. |
Lookup table: gallons by area and waste
All rows at 100 square feet per gallon. Find your area and waste level, read across to the exact figure and the order.
| Area | Waste | Needed area | Exact gallons | Order |
|---|---|---|---|---|
| 100 sq ft | 0% | 100.00 sq ft | 1.00 | 1 gallon |
| 100 sq ft | 5% | 105.00 sq ft | 1.05 | 2 gallons |
| 100 sq ft | 10% | 110.00 sq ft | 1.10 | 2 gallons |
| 100 sq ft | 15% | 115.00 sq ft | 1.15 | 2 gallons |
| 200 sq ft | 0% | 200.00 sq ft | 2.00 | 2 gallons |
| 200 sq ft | 5% | 210.00 sq ft | 2.10 | 3 gallons |
| 200 sq ft | 10% | 220.00 sq ft | 2.20 | 3 gallons |
| 200 sq ft | 15% | 230.00 sq ft | 2.30 | 3 gallons |
| 400 sq ft | 0% | 400.00 sq ft | 4.00 | 4 gallons |
| 400 sq ft | 5% | 420.00 sq ft | 4.20 | 5 gallons |
| 400 sq ft | 10% | 440.00 sq ft | 4.40 | 5 gallons |
| 400 sq ft | 15% | 460.00 sq ft | 4.60 | 5 gallons |
| 800 sq ft | 0% | 800.00 sq ft | 8.00 | 8 gallons |
| 800 sq ft | 5% | 840.00 sq ft | 8.40 | 9 gallons |
| 800 sq ft | 10% | 880.00 sq ft | 8.80 | 9 gallons |
| 800 sq ft | 15% | 920.00 sq ft | 9.20 | 10 gallons |
Who uses this
- A homeowner finishing one room — 400 square feet at 10% waste is 4.40 gallons exact, order 5 — the lookup table covers the room sizes around it without touching the calculator.
- A drywall finisher pricing a job — the coverage and waste branches price an extra coat or rougher joints at once, so a quote can be adjusted before the buckets are ordered.
- A builder ordering for a whole house — the 800-square-foot rows scale the same model, and the reverses recover the area, coverage or waste behind any quoted gallon count.
- A DIYer checking a store recommendation — the exact-fit edge shows when an order needs no rounding up, so a recommendation of 4 gallons for 400 square feet at 0% waste can be checked rather than trusted.
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. The main limitation is the inputs, not the arithmetic: whether the area includes every wall and joint, whether the coverage figure matches the coat system actually applied, and whether the waste allowance suits the joint condition are all judgement calls, and this page prices the figures you enter without checking them. This page is a calculation tool, not building advice.
Cite this calculator
400 square feet at 10% waste with 100 square feet per gallon needs 440.00 square feet, 4.40 gallons exact: order 5 gallons. Source: Bright Side Kit, https://brightoolbox.com/joint-compound-chart/, accessed 29 October 2026.
Frequently asked questions
Why order 5 gallons when the exact figure is 4.40?
Because joint compound is sold by the whole gallon and you cannot buy four-tenths of a gallon. Rounding down to 4 would leave 40.00 square feet uncovered; rounding up to 5 covers the full need with six-tenths of a gallon of headroom, which is exactly what the waste allowance is for.
When does the order need no rounding up?
When the needed area divides evenly by the coverage: 400 square feet at 0% waste is 400.00 square feet, which is exactly 4.00 gallons at 100 square feet a gallon, so the order is 4. Exact fits are the exception, not the rule, and they vanish the moment waste is added.
Should waste apply to the area or to the gallons?
To the area. Waste is extra surface to cover — sanding loss, spillage, uneven joints — so it belongs in the needed area before dividing by coverage. Applying waste to the gallons after rounding gives a different, usually smaller, answer that understates the need.
What coverage figure should I use?
The one on the bucket or product sheet for the coat system you are actually applying. A bucket rated at 100 square feet for a standard two-coat system may cover far less with an extra skim coat, and using the wrong coat count is the fastest way to run short mid-wall.
Do I subtract windows and doors?
Only openings you genuinely will not finish. A door or window opening saves the flat area but adds corners to finish, so subtracting the full opening without adding the corners back understates the job. When in doubt, leave small openings in and treat the saving as extra headroom.
How is a joint compound chart different from a plaster chart?
Only the material changes: joint compound at 100 square feet per gallon against the plaster page at 80 square feet per bag. The model — area times waste divided by coverage, rounded up — is identical, which is what makes the chart pages comparable.