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Siding chart calculator
Put your area, coverage per box and waste in: 400 square feet at 10% waste with 200 square feet per box is 2.20 boxes exact, order 3.
★ CONSTRUCTION · EXTERIOR · SIDING CHART
Siding Coverage Chart: 3 Boxes for 400 Sq Ft, 10% Waste
On the defaults — 400 square feet at 10% waste with 200 square feet per box coverage — you need 440.00 square feet of siding coverage, 2.20 boxes exact, so order 3 boxes. This is the SIDING version — area times waste divided by coverage, with a lookup table for every common area and waste level — the stucco-chart page is the STUCCO version — the same divide-and-round-up model counted in stucco bags; the plaster-chart page is the PLASTER version — the same model counted in plaster bags; the joint-compound-chart page is the JOINT COMPOUND version — the same model counted in compound gallons; and the thinset-chart page is the THINSET version — the same model counted in thinset bags.
What does 2.20 boxes, order 3, mean?
It means that 400 square feet of wall, once 10% waste is added, needs 440.00 square feet of siding coverage, which is 2.20 boxes at 200 square feet a box — and since siding is sold by the whole box, you order 3. The exact figure and the order figure answer different questions: 2.20 is the arithmetic, 3 is the purchase, and eight-tenths of a box of headroom is comfortable but not generous — which is exactly why the waste allowance matters here, because a wall full of corners or a lower coverage eats it at once. The part people get wrong is ordering the exact figure rounded down: 2.20 rounded down is 2 boxes, 400.00 square feet of coverage against a 440.00-square-foot need, and the last wall runs short. The other part people get wrong is applying the waste percentage to the boxes instead of the area: waste is 10% more surface to cover, not 10% more boxes 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 200 square feet per box really your coverage? Two hundred square feet is the coverage for the profile on the box, and it is the figure the exact-boxes line turns on: the 100-square-foot-coverage branch totals 4.40 boxes exact against the 2.20 headline, so halving the coverage doubles the order on 400 square feet. If your profile overlaps more heavily or your boards are wider than the box assumes, your real coverage is lower and your real box count higher — check the profile on the product sheet against the profile you are actually installing.
Is 10% waste enough for your walls? Ten percent is the waste allowance, and it is the figure the needed-area line turns on: the 20%-waste branch totals 2.40 boxes exact against the 2.20 headline, so doubling waste adds a fifth of a box here and nearly a box on larger jobs. Smooth flat walls at 10% are reasonable; walls full of corners, windows, and angles want 15% or 20%, because every cut end and every uneven surface eats siding 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 4.40 boxes exact against the 2.20 headline, so a missed wall doubles the order. Measure wall by wall, subtract large openings only if you genuinely will not side them, and add the corners and trim — small strips that are easy to forget and add up to a box on a whole house.
Worked example
On the defaults: 400 square feet, 200 square feet per box, 10% waste.
- Needed area: 400 × 1.10 is 440.00 sq ft.
- Exact boxes: 440.00 ÷ 200 is 2.20 boxes.
- Order: 2.20 rounded up is 3 boxes — 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 2.20 boxes is 400 square feet, the coverage behind 2.20 boxes is 200 square feet per box, and the waste behind 2.20 boxes is 10%. With 0% waste the model honestly shows 2.00 boxes exact and an order of 2 — an exact fit, where order equals exact, unlike the headline case where rounding up adds headroom.
Every branch, checked
- 200 square feet, 200 square feet per box, 10% waste: 200 square feet, 200 square feet per box, 10% waste: 1.10 boxes exact — order 2 boxes.
- 800 square feet, 200 square feet per box, 10% waste: 800 square feet, 200 square feet per box, 10% waste: 4.40 boxes exact — order 5 boxes.
- 400 square feet, 100 square feet per box, 10% waste: 400 square feet, 100 square feet per box, 10% waste: 4.40 boxes exact — order 5 boxes.
- 400 square feet, 200 square feet per box, 20% waste: 400 square feet, 200 square feet per box, 20% waste: 2.40 boxes exact — order 3 boxes.
The reverses, worked backwards
- Area behind 2.20 boxes: 400 sq ft — at 400 sq ft the figures are 2.20 boxes exact — order 3 boxes.; at the lower neighbor the figures are 1.93 boxes exact — order 2 boxes.; at the upper neighbor the figures are 2.48 boxes exact — order 3 boxes..
- Coverage behind 2.20 boxes: 200 sq ft per box — at 200 sq ft per box the figures are 2.20 boxes exact — order 3 boxes.; at the lower neighbor the figures are 2.44 boxes exact — order 3 boxes.; at the upper neighbor the figures are 2.00 boxes exact — order 2 boxes..
- Waste behind 2.20 boxes: 10% waste — at 10% waste the figures are 2.20 boxes exact — order 3 boxes.; at the lower neighbor the figures are 2.10 boxes exact — order 3 boxes.; at the upper neighbor the figures are 2.30 boxes exact — order 3 boxes..
What the defaults assume
The defaults are 400 square feet, 200 square feet per box and 10% waste, so the headline is one medium wall area of siding at a standard profile 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 boxes are needed area divided by coverage, and the order is exact boxes rounded up to the next whole box, guarded by a 1e-12 epsilon so a true exact fit orders exactly that count rather than one more 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 0.28 boxes; the coverage reverse is checked at 20 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 0.10 boxes. The model does not include trim, starter strips, J-channels, or different products for different walls — 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 boxes | needed area ÷ coverage per box | 2.20 boxes — 440.00 ÷ 200. |
| Order | exact boxes rounded up (1e-12 epsilon guard) | 3 boxes — 2.20 rounds up to the next whole box. |
| Area behind a target exact figure | exact boxes × coverage ÷ (1 + waste ÷ 100) | 400 sq ft — 2.20 × 200 ÷ 1.10. |
| Coverage behind a target exact figure | needed area ÷ exact boxes | 200 sq ft per box — 440.00 ÷ 2.20. |
| Waste behind a target exact figure | (exact boxes × coverage ÷ area − 1) × 100 | 10% — (2.20 × 200 ÷ 400 − 1) × 100. |
| Headroom in the order | order − exact boxes | 0.80 boxes — 3 − 2.20, comfortable headroom that waste alone must protect. |
| 200 square feet, 200 square feet per box, 10% waste | same model | 1.10 boxes exact — order 2 boxes. |
| 800 square feet, 200 square feet per box, 10% waste | same model | 4.40 boxes exact — order 5 boxes. |
| 400 square feet, 100 square feet per box, 10% waste | same model | 4.40 boxes exact — order 5 boxes. |
| 400 square feet, 200 square feet per box, 20% waste | same model | 2.40 boxes exact — order 3 boxes. |
| Area behind 2.20 boxes | reverse | 400 sq ft: 2.20 boxes exact — order 3 boxes. |
| Coverage behind 2.20 boxes | reverse | 200 sq ft per box: 2.20 boxes exact — order 3 boxes. |
| Waste behind 2.20 boxes | reverse | 10% waste: 2.20 boxes exact — order 3 boxes. |
| 0 square feet | same model | 0.00 boxes exact — order 0 boxes. |
| Negative area | same model | Area — 0 or more. |
| Zero coverage | same model | Coverage — more than 0. |
| 400 square feet, 0% waste | same model | 2.00 boxes exact — order 2 boxes. |
Lookup table: boxes by area and waste
All rows at 200 square feet per box. Find your area and waste level, read across to the exact figure and the order.
| Area | Waste | Needed area | Exact boxes | Order |
|---|---|---|---|---|
| 100 sq ft | 0% | 100.00 sq ft | 0.50 | 1 box |
| 100 sq ft | 5% | 105.00 sq ft | 0.53 | 1 box |
| 100 sq ft | 10% | 110.00 sq ft | 0.55 | 1 box |
| 100 sq ft | 15% | 115.00 sq ft | 0.58 | 1 box |
| 200 sq ft | 0% | 200.00 sq ft | 1.00 | 1 box |
| 200 sq ft | 5% | 210.00 sq ft | 1.05 | 2 boxes |
| 200 sq ft | 10% | 220.00 sq ft | 1.10 | 2 boxes |
| 200 sq ft | 15% | 230.00 sq ft | 1.15 | 2 boxes |
| 400 sq ft | 0% | 400.00 sq ft | 2.00 | 2 boxes |
| 400 sq ft | 5% | 420.00 sq ft | 2.10 | 3 boxes |
| 400 sq ft | 10% | 440.00 sq ft | 2.20 | 3 boxes |
| 400 sq ft | 15% | 460.00 sq ft | 2.30 | 3 boxes |
| 800 sq ft | 0% | 800.00 sq ft | 4.00 | 4 boxes |
| 800 sq ft | 5% | 840.00 sq ft | 4.20 | 5 boxes |
| 800 sq ft | 10% | 880.00 sq ft | 4.40 | 5 boxes |
| 800 sq ft | 15% | 920.00 sq ft | 4.60 | 5 boxes |
Who uses this
- A homeowner siding one wall area — 400 square feet at 10% waste is 2.20 boxes exact, order 3 — the lookup table covers the areas around it without touching the calculator.
- A siding contractor pricing a job — the coverage and waste branches price a different profile or rougher walls at once, so a quote can be adjusted before the boxes 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 box count.
- A DIYer checking a store recommendation — the headroom note shows why 3 boxes for 400 square feet leaves comfortable slack, so a recommendation of 2 boxes 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 reveal, whether the coverage figure matches the profile actually installed, and whether the waste allowance suits the wall 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 200 square feet per box needs 440.00 square feet, 2.20 boxes exact: order 3 boxes. Source: Bright Side Kit, https://brightoolbox.com/siding-chart/, accessed 29 October 2026.
Frequently asked questions
Why order 3 boxes when the exact figure is 2.20?
Because siding is sold by the whole box and you cannot buy two-tenths of a box. Rounding down to 2 would leave 40.00 square feet uncovered; rounding up to 3 covers the full need with eight-tenths of a box of headroom, which is why the waste allowance must be honest on this material.
When does the order need no rounding up?
When the needed area divides evenly by the coverage: 400 square feet at 0% waste is exactly 2.00 boxes at 200 square feet a box, so the order is 2. 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 boxes?
To the area. Waste is extra surface to cover — cutting, trimming, uneven walls — so it belongs in the needed area before dividing by coverage. Applying waste to the boxes after rounding gives a different, usually smaller, answer that understates the need.
What coverage figure should I use?
The one on the box or product sheet for the profile you are actually installing. A box rated at 200 square feet for one profile may cover far less with a wider board or heavier overlap, and using the wrong profile is the fastest way to run short mid-wall.
Do I subtract windows and doors?
Only openings you genuinely will not side. A door or window opening saves the flat area but adds trim to finish, so subtracting the full opening without adding the trim back understates the job. When in doubt, leave small openings in and treat the saving as extra headroom.
How is a siding chart different from a stucco chart?
Only the material changes: siding at 200 square feet per box against the stucco page at 90 square feet per bag. The model — area times waste divided by coverage, rounded up — is identical, which is what makes the chart pages comparable.