Grout Calculator
Grout calculator for sanded, unsanded or epoxy, from tile size, joint width and area. Takes hexagon and penny round, not just rectangles, and handles a part regrout.
By CalcBuilt Editorial TeamUpdated September 14, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Grout needed
- 5.9 lb
- Including 15% waste, filled the full 0.375 in tile thickness. Manufacturer coverage charts run more conservative, so check the bag.
- Bags to buy
- 1 x 10 lb or 1 x 25 lb
- Both stocked sizes, since a supplier rarely has only the one you picked. Sanded grout suits this joint width, and unsanded on polished marble or glass regardless. Colour shifts between lots, so buy every bag from one lot number and mix each batch with the same measured water
- Joint volume
- 0.059 cu ft
- 102 cu in at 0.125 in wide, filled the full 0.375 in tile thickness
- Tiles covered
- 78 tiles
- 12 in x 12 in tile over 80 sq ft, with joints 2.1% of the surface
Grout formula
Grout fraction = 1 - (tile face area / cell area), where the cell is one tile plus its share of the joints around it
Rectangle: cell = (Tile width + joint) x (Tile length + joint), face = width x length
Hexagon: cell = 0.866 x (across the flats + joint) squared, face = 0.866 x across the flats squared
Penny round: cell = 0.866 x (diameter + joint) squared, face = 3.1416 x (diameter / 2) squared, which makes a 1 in penny round floor 28% grout
Joint volume (cu in) = Area (sq in) x Grout fraction x fill depth
Tiles = Area (sq in) / cell area
Regrout: fill depth is what you raked out, not the tile thickness, so a 1/8 in rake of a 3/8 in tile is a third of the volume
Grout (lb) = Joint volume x 0.0578 lb per cu in x (1 + waste %)
Bags = Grout (lb) / bag size, rounded up
Epoxy: gallon units = Joint volume / 231 cu in, since a kit is sold by volume and mixed all at once
Silicone = Joint length x 12 x joint width squared / 18.05 cu in per 10 fl oz tubeWorked example
A 12 x 12 ft kitchen floor in 12 x 24 in porcelain, 3/8 in thick with 3/16 in joints: 144 sq ft x 144 = 20,736 sq in. Each tile sits in a cell of 12.1875 x 24.1875 = 294.8 sq in and covers 288 of it, so the joints are 1 - 288 / 294.8 = 2.3% of the floor and there are 70.3 tiles. Joint volume = 20,736 x 0.023 x 0.375 = 179 cu in.
Grout = 179 x 0.0578 = 10.3 lb, plus 15% waste = 11.9 lb. Buy one 25 lb bag or two 10 lb bags.
Quick reference
| Tile size | Tiles per 100 sq ft | Grout |
|---|---|---|
| 3 x 6 in | 752 | 18.6 lb |
| 4 x 4 in | 846 | 18.6 lb |
| 6 x 6 in | 384 | 12.6 lb |
| 12 x 12 in | 98 | 6.4 lb |
| 12 x 24 in | 49 | 4.8 lb |
| 18 x 18 in | 44 | 4.3 lb |
| 24 x 24 in | 25 | 3.2 lb |
How to calculate grout
Grout fills whatever the tile does not cover, so the amount depends on the tile size, the tile shape, the joint width and the tile thickness, not just the floor area. Small tiles like 3 x 6 subway or 4 x 4 have far more joint per square foot than 12 x 24 planks. Figure about 18.6 lb per 100 sq ft versus 4.8 lb. Thicker tile and wider joints scale the amount up in proportion.
Shape is the part most calculators skip, because manufacturer coverage charts are indexed by a nominal rectangular size. Squares and rectangles meet edge to edge, so the joint is a line of constant width and the grout is a small percentage of the floor: 2.1% for 12 x 12 in tile at 1/8 inch joints. Hexagons and penny rounds do not, so the grout also fills the corner each tile misses. A 1 inch penny round floor is 28% grout, which is fourteen times the fraction, and entering it as a 1 x 1 inch square returns a quarter less than the job takes. Pattern is the opposite case: running bond, herringbone and a 33% offset all change no volume at all, because every tile keeps its perimeter and every joint is still shared by two tiles.
This calculator works from the joint geometry and a dry density of about 100 lb per cubic foot. Manufacturer coverage charts assume more waste and fuller joints and usually show less coverage per bag, so if the chart on the bag disagrees, trust the chart. Color is the reason to buy the whole job at once. Pigment shifts between lots and with the mix water, so buy every bag from one lot number and measure the water.
Sanded, unsanded and epoxy grout
Sanded cement grout is for joints 1/8 inch and wider; the sand keeps it from shrinking and cracking. Unsanded grout is for joints under 1/8 inch and for polished marble, glass and metal tile that sand would scratch. Fine-aggregate grouts such as Mapei Ultracolor Plus FA and Custom Prism cover both ranges, cure fast and resist stains without sealer, at about twice the price per bag. Changes of plane get no grout at all. Inside corners, the tub and shower pan line, and the tile-to-countertop joint are movement joints; fill them with 100 percent silicone or a color-matched sealant (TCNA EJ171).
Epoxy grout (Laticrete SpectraLOCK, Mapei Kerapoxy) comes in kits rated by square feet and costs several times more. It is stain-proof with no sealer, which earns its price on shower floors and backsplashes. It sets in 45 to 80 minutes and haze left overnight is permanent; work 15 to 20 square feet at a time with a second person sponging. Cement grout is different: keep water off it for 24 hours, mist it in a hot dry room, and seal it after 48 to 72 hours. White powder on a cured joint is efflorescence, salts carried by too much mix water or by moisture under the tile. It wipes off with the same acid cleaner; if it keeps coming back, the slab is wet.
What this calculator leaves out
Grout only. Not included: the silicone or color-matched sealant for every change of plane, about one 10 oz tube per 40 to 50 feet of joint. Also left out: penetrating sealer for cement grout, haze remover, a grout release for textured tile, and a float, sponges and buckets. Thinset, backer board and the tile itself have their own calculators.
Mistakes that cost money
- Sanded grout on polished marble, glass or metal tile scratches the face; use unsanded or a fine-aggregate grout such as Ultracolor Plus FA.
- Two lot numbers or eyeballed mix water give two shades of one color; buy every bag from one lot and measure the water.
- Cement haze left overnight needs a sulfamic acid remover after 3 days (never on marble); epoxy haze left overnight never comes off.
- Grouting the inside corners, tub line and tile-to-counter joint: those are movement joints and crack; fill them with 100% silicone (TCNA EJ171).
- Sealing before the grout cures traps water and turns it white; wait 48 to 72 hours or the time on the bag, and skip epoxy.
- Too much water in the mix or a dripping sponge washes out pigment and leaves a weak, powdery joint; wring the sponge nearly dry.
Key facts
- A regrout refills only what was raked out. Raking 1/8 in from a 3/8 in tile is a third of the original joint volume, so the same floor takes 2 lb instead of 5.9.
- Use sanded grout for joints 1/8 in and wider and unsanded grout for joints narrower than 1/8 in.
- Dry grout weighs about 100 lb per cubic foot, so 1 lb fills about 17 cubic inches of joint.
- Larger tiles need far less grout: 12 x 12 in tile takes about 6.4 lb per 100 sq ft and 4 x 4 in tile about 18.6 lb, at 1/8 in joints.
- Shape counts for more than size at the small end. A 1 in penny round floor is 28% grout by area and takes about 59 lb per 100 sq ft at 1/4 in thick; 1 in squares over the same floor take 44 lb, because squares meet edge to edge and circles do not.
- Typical joint widths are 1/16 in on small rectified porcelain, 1/8 to 3/16 in for ceramic and large format, and 1/4 in for tumbled stone.
- Cement grout should cure 48 to 72 hours before it is sealed.
Frequently asked questions
How much epoxy grout do I need?
Work out the joint volume the same way, then divide by the yield printed on the kit rather than by a weight. Epoxy is sold by the unit and a full kit has to be mixed at once, so a part used unit is a part wasted one. This calculator gives the volume and a gallon count for that reason.
How much grout do I need for 100 square feet of 12x12 tile?
About 6.4 lb with 1/8 inch joints and 3/8 inch thick tile, or 7.4 lb with 15% waste. One 10 lb bag covers it.
How much grout does hex or penny round tile need?
Far more than a square of the same nominal size, because the tiles do not meet edge to edge and the grout fills the corners between them. Set the tile shape above rather than entering the tile as a rectangle: 100 sq ft of 1 in penny round at 1/4 inch thick takes about 59 lb, where the same floor entered as 1 x 1 inch squares comes back at 44 lb, a quarter light. A 4 inch hexagon runs about 6% over the rectangle answer. Hexagons are sold both ways, so check whether the size on the box is across the flats or across the points; multiply across the points by 0.866 to get across the flats.
How much does a 25 lb bag of grout cover?
It depends on the tile. At 1/8 inch joints with 15% waste, a 25 lb bag covers about 340 sq ft of 12 x 12 in tile. The same bag covers only about 120 sq ft of 4 x 4 in tile. Manufacturer charts are more conservative and often show about half those figures.
Is epoxy grout worth the extra cost?
For a shower floor, a kitchen backsplash or a white floor, usually yes: it is stain-proof, never needs sealing and does not feed mold. Kits cost several times more per square foot and set in under an hour, so it is slow, unforgiving work. For a bedroom or hallway floor, a high-performance cement grout such as Ultracolor Plus FA gets most of the benefit for half the money.
How long before grout can get wet?
Keep water off it for 24 hours and traffic light for 72 hours; in a hot, dry room mist it so it cures instead of drying out. Apply a penetrating sealer to cement grout after 48 to 72 hours of curing.
Sources and references
- Polyblend Plus Sanded Grout coverage chart by tile size and joint width (Custom Building Products)
- Polyblend Sanded Grout technical data sheet TDS-129 (Custom Building Products)
- Ultracolor Plus FA grout product page and coverage (Mapei)
Next steps for this project
The usual order for a flooring & tile project. See all flooring & tile calculators.
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Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.