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Grout calculator
Put your floor size, coverage per bag and waste in: a 10 ft by 8 ft floor is 80 sq ft — 88 sq ft with 10% waste, 2 bags at 50 sq ft per bag.
★ CONSTRUCTION · TILE · GROUT
Grout Calculator: 2 Bags for a 10×8 ft Tiled Floor
On the defaults — a 10 ft by 8 ft floor, 50 sq ft per bag, 10% waste — you need 2 bags of grout. This is the grout tool: measure the floor once, allow for the wash-off, and order the bags once — a half-grouted floor waits for no second bag.
What does grout needed 2 bags mean?
It means two bags of grout fill the joints of a 10 ft by 8 ft tiled floor once wash-off waste is allowed for. The floor itself is 10 times 8, or 80 square feet; with 10% waste that becomes 88 square feet of grouting, and at 50 sq ft per bag the exact count is 1.76 bags, which rounds up to 2 whole bags because grout is sold by the bag, not by the three-quarter. The second bag is not spare stock exactly — it is the grout the job consumes in washing off and re-grouting, so a floor ordered to the exact drop runs dry before the last joints.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Floor area | length × width | 80 sq ft — 10 × 8. |
| Area with waste | floor area × (1 + waste ÷ 100) | 88 sq ft — 80 × 1.10. |
| Bags | area with waste ÷ coverage per bag, rounded up | 2 bags — 88 ÷ 50, rounded up. |
Three things to check before you trust the number
First, check the coverage figure on the bag label: 50 sq ft per bag is a planning figure for standard joints, but wide joints and small tiles cover less — at 25 sq ft per bag this floor needs 4 bags, not 2. Second, measure the tiled area only, not the room around it: the count follows the area that is actually grouted. Third, judge the waste honestly: a pro on a straight floor fits 10%, but a first-time tiler, or a floor with many cuts and corners, can want 15%, since every wash-off takes grout with it.
Worked example
10 ft long, 8 ft wide, 50 sq ft per bag, 10% waste. Floor area: 10 × 8 = 80 sq ft. With waste: 80 × 1.10 = 88 sq ft. Bags: 88 ÷ 50 = 1.76, rounded up to 2 bags. In practice that means ordering 2 bags, and expecting the second bag to go on the wash-off and the touch-ups. If the same floor used 25 sq ft per bag instead, the need would rise to 4 bags with waste, but the floor covered would be identical.
Every branch, checked
With a 15 ft long floor instead of 10 ft, the area rises to 120 sq ft and the need to 3 bags with waste. With a 10 ft wide floor, the area rises to 100 sq ft and the need to 3 bags with waste. With 100 sq ft per bag, the area stays 80 sq ft but the need falls to 1 bag with waste. With 50% waste, the area stays 80 sq ft but the need rises to 3 bags with waste. Area, coverage and waste each move the count on their own, so a wrong coverage figure is as costly as a wrong measurement.
The reverses, worked backwards
The length behind 2 bags is 10 ft: at 5 ft the need is 1 bag (40 sq ft floor, 50 sq ft per bag, 10% waste); at 15 ft it is 3 bags (120 sq ft floor, 50 sq ft per bag, 10% waste). The width behind 2 bags is 8 ft: at 4 ft the need is 1 bag (40 sq ft floor, 50 sq ft per bag, 10% waste); at 10 ft it is 3 bags (100 sq ft floor, 50 sq ft per bag, 10% waste). The coverage behind 2 bags is 50: at 25 the need is 4 bags (80 sq ft floor, 25 sq ft per bag, 10% waste); at 100 it is 1 bag (80 sq ft floor, 100 sq ft per bag, 10% waste). Each reverse moves one input and holds the rest, so the step is exactly one dimension or one coverage change.
What the defaults assume
The defaults assume a 10 ft by 8 ft rectangular tiled floor, standard joints at 50 sq ft per bag, and 10% waste. They do not assume the tiles themselves, the adhesive, a second colour of grout for a border, or the sealer — a floor with a border course needs that grout counted separately, and sealer is bought by the bottle, not by the bag.
Who uses this
- A homeowner grouting a bathroom floor: the 2-bag order settles the merchant call before the first joint is filled.
- A DIY tiler finishing a kitchen floor: the same maths on the floor alone gives the bags, not a whole house.
- A tiler quoting a job: area, coverage, waste — the quote follows the same three steps, and the waste line shows the client why.
- A landlord refreshing a rental bathroom: the floor size off the plans, divided by coverage, gives the grout line on the refresh budget.
Accuracy & limitations
The arithmetic is exact for the inputs entered; the judgement is the coverage-per-bag figure and the waste allowance. Real floors have cuts, corners and different joint widths, and the joint width changes the grout per square foot more than the tile size does; a floor measured gross over-orders, and a coverage figure read off a different joint width under-orders. Treat 2 bags as the planning order for a straight 10 ft by 8 ft floor at 50 sq ft per bag, and raise the waste to 15% for a first-time tiler or a floor with many cuts.
Cite this calculator
Bright Side Kit, “Grout Calculator: 2 Bags for a 10×8 ft Tiled Floor”, https://brightoolbox.com/grout-calculator/, accessed 3 November 2026. Students and researchers: cite the calculator name, the page URL and the date you used it, and quote the defaults (10 ft × 8 ft floor, 50 sq ft per bag, 10% waste) so the 2-bag result can be checked.
Frequently asked questions
How many bags of grout do I need for a 10×8 floor?
2 bags at 50 sq ft per bag with 10% waste. The floor is 80 sq ft; with waste that is 88 sq ft, and 88 ÷ 50 = 1.76, rounded up to 2.
How much area does a bag of grout cover?
Commonly around 50 sq ft for standard joints, which is the figure this calculator uses. Wide joints and small tiles cover less — check the bag label and lower the figure for thirsty joints.
How much waste should I allow for grout?
10% for a straight floor grouted by an experienced hand, 15% for a first-time tiler or a floor with many cuts. Waste is the wash-off and re-grouting, not spare stock.
Does this count the tiles and adhesive too?
No — this calculator counts grout bags only. The tile calculator counts the tiles for the same floor, and the adhesive is bought separately again.
Should I buy the exact bags or round up?
Round up: grout is sold by the bag, and the spare bag is the touch-up stock. A floor grouted to the exact drop leaves nothing for a cracked joint next year.
Do I need to seal the grout after?
Sealer is optional but recommended in wet rooms, and it is bought by the bottle, not counted here. The mortar calculator sizes the wall mortar on the same area-times-rate logic, for the walls around the floor.