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Thinset chart
Put your area, coverage per bag and waste allowance in: 400 sq ft at 10% waste needs 8.80 bags exact, order 9.
★ CONSTRUCTION · TILE · COVERAGE CHART
Thinset Chart: 9 Bags for 400 Sq Ft Floor at 10% Waste
On the defaults — 400 square feet at 10% waste with 50 square feet per bag coverage — you need 440.00 square feet of thinset coverage, 8.80 bags exact, so order 9 bags. This is the THINSET version — area times waste divided by coverage, with a lookup table for every common area and bag coverage — the mortar-chart page is the MORTAR version — the same divide-and-round-up model counted in mortar bags; the underlayment-chart page is the UNDERLAYMENT version — the same model counted in underlayment sheets; the backer-board-chart page is the BACKER-BOARD version — the same model counted in backer-board sheets; and the paint-chart page is the PAINT version — the same model counted in topcoat gallons.
What does 8.80 bags, order 9, mean?
It means that 400 square feet of tile, with a 10% waste allowance, need 440.00 square feet of thinset coverage, and at 50 square feet per bag that is 8.80 bags — eight full bags plus four fifths of a ninth — and because thinset is sold by the bag, you order 9. The rounding is the whole story in miniature: a partial bag cannot be bought in the quantity needed, so any fraction, however small, becomes a whole bag. The part people get wrong is rounding to the nearest bag instead of up: 8.80 rounded to the nearest is 9 here, which happens to be right, but 8.25 rounded to the nearest is 8, and 8 bags cover only 400 square feet, leaving 40.00 square feet without thinset. The other part people get wrong is the exact fit: 440 square feet of coverage need exactly 1.00 bag at 440 square feet per bag, and order exactly 1, because the rounding is up to the next whole bag, not up plus one — an exact fit needs no spare bag from the rounding, though a spare for spillage is a separate decision.
Three things to check before you trust the number
Is 50 square feet per bag right for your thinset and trowel? Fifty square feet is the figure this page uses, a mid-range figure for a standard bag at a common trowel size. A larger trowel notch lays a thicker bed and covers fewer feet, so the same 400 square feet at 25 square feet per bag would need 17.60 bags, order 18, not 9 — trowel size changes the count completely, even though the area and waste are unchanged. Check your thinset maker’s coverage table for your trowel size and tile size, and enter that figure rather than trusting the default for a different notch.
Did you measure every area? The area entered here must be the total of all tiled surfaces, not the largest single room: a home with 400 square feet downstairs plus bathrooms, halls and backsplashes has more than 400 square feet to tile. The 200-square-foot branch needs 4.40 bags, order 5, against the 8.80-bag headline, so missing one room understates the order by whole bags on a bigger job. Measure every area, add them before dividing, and do not subtract small gaps unless your thinset maker says to.
Are you counting waste, or a second coat? This page adds 10% for waste — cuts, breakage, spillage and fitting around fixtures — 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 17.60 bags, order 18. Treating a second coat as waste, or waste as a second coat, misstates the order by whole bags either way, so decide the coats first and let the waste percentage stay at waste.
Worked example
On the defaults: 400 square feet, 50 square feet per bag, 10% waste.
- Needed area: 400 × 1.10 is 440.00 square feet.
- Exact bags: 440.00 ÷ 50 is 8.80 bags.
- Order: 8.80 rounded up is 9 bags — the 0.80 is four fifths of a bag that must be bought whole.
- Check: 9 bags cover 450 square feet, which is more than the 440.00 needed; 8 bags cover only 400, which is not enough.
And the other way: the area behind 8.80 bags is 400 square feet, the coverage behind 8.80 bags is 50 square feet per bag, and the waste behind 8.80 bags is 10%. A job at 440 square feet per bag orders exactly 1 bag, and a 500-square-foot job at 50 square feet per bag and 10% waste lands exactly on 11.00 bags, order 11.
Every branch, checked
- 200 square feet, 50 square feet per bag, 10% waste: 200 square feet, 50 square feet per bag, 10% waste: 4.40 bags exact — order 5 bags.
- 800 square feet, 50 square feet per bag, 10% waste: 800 square feet, 50 square feet per bag, 10% waste: 17.60 bags exact — order 18 bags.
- 400 square feet, 25 square feet per bag, 10% waste: 400 square feet, 25 square feet per bag, 10% waste: 17.60 bags exact — order 18 bags.
- 400 square feet, 50 square feet per bag, 20% waste: 400 square feet, 50 square feet per bag, 20% waste: 9.60 bags exact — order 10 bags.
The reverses, worked backwards
- Area behind 8.80 bags: 400 sq ft — at 400 sq ft the figures are 8.80 bags exact — order 9 bags.; at the lower neighbor the figures are 7.70 bags exact — order 8 bags.; at the upper neighbor the figures are 9.90 bags exact — order 10 bags..
- Coverage behind 8.80 bags: 50 sq ft per bag — at 50 sq ft per bag the figures are 8.80 bags exact — order 9 bags.; at the lower neighbor the figures are 11.00 bags exact — order 11 bags.; at the upper neighbor the figures are 7.33 bags exact — order 8 bags..
- Waste behind 8.80 bags: 10% waste — at 10% waste the figures are 8.80 bags exact — order 9 bags.; at the lower neighbor the figures are 8.40 bags exact — order 9 bags.; at the upper neighbor the figures are 9.20 bags exact — order 10 bags..
What the defaults assume
The defaults are 400 square feet, 50 square feet per bag and 10% waste, so the headline is one coat of thinset over a medium tiled floor at a common trowel size. The model is a multiplication, a division and a ceiling: needed area is area times one plus the waste percentage, exact bags are needed area divided by coverage per bag, and the order rounds exact bags up to the next whole bag, with a 1e-12 epsilon so an exact whole number orders exactly that many. Bag coverage differs by trowel — the 50-square-feet figure is mid-range, and a larger notch covers fewer feet, so enter the coverage for the bag and trowel you will actually use. The area reverse is checked at 50 square feet either side, because 50 square feet at 10% waste is 55 square feet, about 1.10 bags; the coverage reverse is checked at 10 square feet either side, because 440.00 over 40 is 11.00 bags and over 60 is 7.33; the waste reverse is checked at 5% either side, because 5% of 400 is 20 square feet, about 0.40 bags. The model does not include second coats, grout, backer board, fasteners, or tools — count those separately.
Lookup table: bags by area and coverage
Each row already includes the 10% waste allowance: needed area is the area times 1.10, exact bags are needed area divided by the coverage in that row, and the order column rounds up. A row that lands exactly on a whole number orders exactly that many — no extra bag is added for an exact fit. For a different trowel size, enter your own coverage in the calculator above: a larger notch covers fewer feet, so the order rises.
| Area | Coverage per bag | Needed area | Exact bags | Order |
|---|---|---|---|---|
| 100 sq ft | 25 sq ft per bag | 110.00 sq ft | 4.40 | 5 bags |
| 100 sq ft | 50 sq ft per bag | 110.00 sq ft | 2.20 | 3 bags |
| 100 sq ft | 75 sq ft per bag | 110.00 sq ft | 1.47 | 2 bags |
| 100 sq ft | 100 sq ft per bag | 110.00 sq ft | 1.10 | 2 bags |
| 200 sq ft | 25 sq ft per bag | 220.00 sq ft | 8.80 | 9 bags |
| 200 sq ft | 50 sq ft per bag | 220.00 sq ft | 4.40 | 5 bags |
| 200 sq ft | 75 sq ft per bag | 220.00 sq ft | 2.93 | 3 bags |
| 200 sq ft | 100 sq ft per bag | 220.00 sq ft | 2.20 | 3 bags |
| 400 sq ft | 25 sq ft per bag | 440.00 sq ft | 17.60 | 18 bags |
| 400 sq ft | 50 sq ft per bag | 440.00 sq ft | 8.80 | 9 bags |
| 400 sq ft | 75 sq ft per bag | 440.00 sq ft | 5.87 | 6 bags |
| 400 sq ft | 100 sq ft per bag | 440.00 sq ft | 4.40 | 5 bags |
| 800 sq ft | 25 sq ft per bag | 880.00 sq ft | 35.20 | 36 bags |
| 800 sq ft | 50 sq ft per bag | 880.00 sq ft | 17.60 | 18 bags |
| 800 sq ft | 75 sq ft per bag | 880.00 sq ft | 11.73 | 12 bags |
| 800 sq ft | 100 sq ft per bag | 880.00 sq ft | 8.80 | 9 bags |
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Needed area | area × (1 + waste ÷ 100) | 440.00 sq ft — 400 × 1.10. |
| Exact bags | needed area ÷ coverage per bag | 8.80 bags — 440.00 ÷ 50. |
| Order | exact bags rounded up | 9 bags — 8.80 rounds up. |
| Area behind a target exact figure | exact bags × coverage per bag ÷ (1 + waste ÷ 100) | 400 sq ft — 8.80 × 50 ÷ 1.10. |
| Coverage behind a target exact figure | needed area ÷ exact bags | 50 sq ft per bag — 440.00 ÷ 8.80. |
| Square feet covered by the order | order × coverage per bag | 450 sq ft — 9 × 50, more than the 440.00 needed. |
| Square feet short on one fewer bag | needed area − (order − 1) × coverage per bag | 40.00 sq ft — 440.00 − 8 × 50, which is why rounding down fails. |
| 200 square feet, 50 square feet per bag, 10% waste | same model | 4.40 bags exact — order 5 bags. |
| 800 square feet, 50 square feet per bag, 10% waste | same model | 17.60 bags exact — order 18 bags. |
| 400 square feet, 25 square feet per bag, 10% waste | same model | 17.60 bags exact — order 18 bags. |
| 400 square feet, 50 square feet per bag, 20% waste | same model | 9.60 bags exact — order 10 bags. |
| Area behind 8.80 bags | reverse | 400 sq ft: 8.80 bags exact — order 9 bags. |
| Coverage behind 8.80 bags | reverse | 50 sq ft per bag: 8.80 bags exact — order 9 bags. |
| Waste behind 8.80 bags | reverse | 10% waste: 8.80 bags exact — order 9 bags. |
| 0 square feet | same model | 0.00 bags exact — order 0 bags. |
| Negative area | same model | Area — 0 or more. |
| Zero coverage | same model | Coverage — more than 0. |
| 440 square feet per bag | same model | 1.00 bags exact — order 1 bags. |
Who uses this
- A DIYer tiling a new floor — 400 square feet at 10% waste is 9 bags, with the lookup table covering every other area and bag coverage without re-measuring.
- A tile installer ordering for a job — the branches show how the order moves with area, coverage and waste, so a different trowel size is repriced before ordering.
- A homeowner comparing trowel sizes — the 25-square-feet branch shows what a larger notch really costs in bags, before the job starts.
- An estimator checking a quote — the reverses recover the area, coverage or waste behind any quoted bag 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: bag coverage varies widely with trowel size and tile size — a large notch lays a thicker bed and covers far fewer feet than a small one — so check your thinset maker’s coverage table for your trowel and enter your own figure when your notch differs. This page is a calculation tool, not trade advice — follow the thinset maker’s instructions for mixing, open time and curing.
Cite this calculator
400 square feet of tile at 10% waste with 50 square feet per bag coverage needs 440.00 square feet, 8.80 bags exact: order 9 bags. Source: Bright Side Kit, https://brightoolbox.com/thinset-chart/, accessed 29 October 2026.
Frequently asked questions
How many square feet does one bag of thinset cover?
This page uses 50 square feet per bag, a mid-range figure for a standard bag at a common trowel size. A larger trowel notch lays a thicker bed and covers fewer feet, so the same 400 square feet at 25 square feet per bag needs 17.60 bags, order 18 — the calculator divides by whatever you enter, so the answer stays honest for your trowel size.
Is thinset the same as mortar?
Thinset is a type of mortar, but the two are not interchangeable in every job: thinset is a cement-based adhesive made for bonding tile to a surface, while general mortar is made for laying brick and block. Both are sold by the bag and both use the same divide-and-round-up arithmetic, which is why the coverage figure, not the product name, decides the order.
Why add 10% waste?
Because material is lost to cuts, breakage, spillage and fitting around fixtures: the 10% allowance covers the thinset that never ends up as a finished bed. Without it, a job that computes to exactly 8.00 bags would run dry on the last stretch of floor, and the waste percentage is what keeps the order honest for real fitting.
Why round up instead of to the nearest bag?
Because a partial bag cannot be bought in the quantity needed, and rounding down leaves floor uncovered: 8.80 bags rounded to the nearest is 9, which happens to be right, but 8.25 rounded to the nearest is 8, and 8 bags cover only 400 of the 440.00 square feet needed. Rounding up guarantees the whole area is covered; the extra fraction is the price of buying whole bags.
What if the exact figure is already a whole number?
Then you order exactly that many: a job at 440 square feet per bag needs exactly 1.00 bag and orders 1, not 2, and the epsilon in the rounding protects exact fits, so a job that lands on a whole number is not charged an extra bag for nothing.
Does the waste allowance cover a second coat?
No: waste and coats are different things. Waste is the extra 10% for cuts, breakage and fitting 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 17.60 bags, order 18. Decide the coats first, then let waste stay at waste.