Grout Calculator
Grout is the one material nobody estimates correctly, because the quantity depends on the joint, not the floor. Enter four numbers and get kilos, bags, and the small items you will drive back for.
Reviewed · Method: measured area + industry waste allowance, rounded up to real package sizes · How the numbers are calculated
Enter your dimensions and hit Calculate my grout. You will get the quantity, the buyable quantity, a shopping list, and a budget range.
Figure. Grout depends on joint width and depth, not on floor area alone. Two rooms of the same size take different amounts of grout.
Figure. Joint width is set by the spacer you choose. A 3 mm joint and a 6 mm joint are not the same job.
Why grout cannot be estimated from floor area alone
Two rooms of the same size can need grout in a ratio of three to one. What changes is the joint. A 12x24 inch tile with a 3 mm joint has a small amount of edge length per square foot, so the grout lines are short and thin. A 4x4 inch tile with a 6 mm joint has eight times the edge length and twice the width. Fill rate scales with both. That is why the industry formula multiplies the edge-to-area ratio of the tile by the joint width, the tile thickness, and the density of the grout.
The joint width decision comes before the grout decision
Rectified porcelain, which is cut square at the factory, is usually laid at 2 to 3 mm. Standard ceramic with a slightly rounded edge needs 3 to 5 mm to hide the cushion. Stone and handmade tile often want 5 to 8 mm because the edges are irregular by nature. Wider joints use more grout and also show dirt faster. Narrow joints save material but leave less room for minor size variation between tiles.
Sanded, unsanded, or epoxy
Sanded grout contains fine aggregate and should be used for joints wider than about 3 mm, because the sand keeps the mix from shrinking and cracking as it cures. Unsanded grout is for tight joints and for scratch-prone surfaces such as polished marble. Epoxy grout is a different product entirely: it does not need sealing, resists stains, and costs roughly four times as much. It is sold in kits sized to a stated area rather than in kilos, so the bag count on this page does not apply to it.
What else goes in the cart
The calculator returns a rubber-faced float, two large-pore sponges, a bucket, a mixing paddle, and sealer. Those are not padding. Grout mixed in a bucket with a drill paddle needs a paddle with the right diameter, or the powder balls up at the bottom. Two sponges matter because a loaded sponge smears haze across the tile face, and rinsing one while using the other is faster than stopping to clean. Sealer is only necessary on cementitious grout in wet areas or on porous tile, but on a shower floor it is not optional.
The grout formula, in plain terms
Grout quantity depends on how much joint volume there is per square metre. Long joint lines per unit area means more grout, which is why a 3x6 subway tile needs several times the grout of a 24x48 slab at the same joint width.
The formula multiplies joint length per square metre by joint width and joint depth, then by the dry density of the grout. Depth is usually the tile thickness, so thicker tile means deeper joints and more grout for the same floor.
Epoxy changes the arithmetic
Epoxy grout is sold in kits sized to a coverage range, not in kilos you can scale. It costs roughly four times cementitious grout, does not need sealing, and does not shrink. On a shower floor or a commercial kitchen it is usually the right call despite the price.
The catch is working time. Epoxy sets harder and faster, and once it cures in a joint you are removing it mechanically. Mix small, work fast, and have a second person wiping behind you.
Worked example: 120 sq ft of 12x24 in tile, 3 mm joints
| Tiled area | 120 sq ft = 11.1 m2 |
| Joint width | 3 mm |
| Joint depth | 9 mm, roughly the tile thickness |
| Yield | about 0.32 kg per m2 |
| With 10% waste | 3.9 kg total |
| Bags | 1 bag of 10 kg |
| Budget band | $19 low, $29 mid, $45 high |
Mistakes that cost real money
Buying grout by floor area
Two 120 sq ft floors take different amounts of grout if one is 3x6 subway tile and the other is 24x48 slab. Smaller tiles mean more joint length per square foot, and joint length is what grout fills.
Mixing a whole bag at once
Cementitious grout has a 20 to 30 minute pot life. A 10 kg bag is far more than most people can float and wipe inside that window. Mix in batches sized to what you can actually finish, and never add water to grout that has started to set.
Choosing sanded or unsanded by habit
Use unsanded grout for joints under 1/8 in, sanded for wider joints, with glass and polished stone as their own cases. The wrong choice shows up as scratched tile or a joint that shrinks and cracks.
Skipping the sealer on cementitious grout
Cement grout is porous. In a shower or on a kitchen floor it stains within months if it is not sealed. Sealer is 10% of the material cost and doubles the life of the joint.
Cleaning too late or too early
Wipe the haze when the grout has firmed but before it hardens, usually 15 to 30 minutes. Too early pulls grout out of the joint; too late means scraping it off tile edges with a plastic blade and a lot of patience.
Frequently asked questions
How much area does a 10 kg bag of grout cover?
It depends entirely on tile size and joint width. With 12x24 inch tile and a 3 mm joint, a 10 kg bag covers roughly 12 to 15 square metres. With small mosaic tile and a 6 mm joint, the same bag covers under two square metres. Always calculate from the joint, not from the bag label.
Can I use the same grout for floor and wall?
Usually yes for cementitious grout, but check the joint width. Wall tile is often thinner, which reduces the fill, and joints on walls are frequently narrower than 3 mm, which pushes you toward unsanded grout. Mixing one batch for both is fine if the joint widths are within one millimetre of each other.
How long before I can seal new grout?
Cementitious grout should cure for at least 72 hours before sealing, and some manufacturers ask for seven days. Sealing too early traps moisture inside the joint and produces a patchy, cloudy finish that cannot be corrected without stripping the sealer and starting again.
Why did my grout crack along the joint?
Almost always too much water in the mix. Grout mixed to a soupy consistency loses strength and shrinks as it dries, which opens a hairline crack at the joint edge. Mix to the consistency of peanut butter, let it slake for ten minutes, then remix briefly before floating.
Is epoxy grout worth the price?
In a shower, a commercial kitchen, or anywhere grease and staining matter, yes. In a dry bedroom floor it is hard to justify four times the material cost. Epoxy also sets faster and is far less forgiving to install, so the labour difference often exceeds the material difference.