Grout Calculator
How much tile grout to buy, in weight and bags, from the tiled area, the tile size and the joint width and depth.
Result…
How it's calculated
Joint factor = (tile length + tile width) ÷ (tile length × tile width) Grout volume = area × joint factor × joint width × joint depth Weight = volume × density × (1 + waste %) Bags = weight ÷ bag size, rounded up
Estimates the grout to fill the joints of a tiled floor or wall. The joint volume per unit area is (L + W) ÷ (L × W) × joint width × joint depth, the formula grout manufacturers print on their datasheets, where L and W are the tile length and width. In millimetres the result is litres per square metre. Multiplied by the grout's density it gives the weight, and then the bags. Densities differ between cement, epoxy and other grouts, so take the figure from your product's datasheet. For the number of tiles, use the tile calculator.
Your numbers, step by step
About the Grout calculator
This grout calculator estimates how much tile grout to buy for a floor or wall, as a weight and a number of bags. Enter the tiled area, the tile length and width, the joint width and the joint depth, which is usually the tile thickness. It uses the joint-volume formula that grout makers print on their datasheets, such as Mapei's Keracolor FF technical data sheet: (L + W) ÷ (L × W) × joint width × joint depth. With sizes in millimetres, that gives litres per square metre. The volume is turned into weight with the density figure from your own grout's datasheet, which you can change, and a waste allowance is added before rounding up to whole bags. Metric and imperial both work, and the steps show every number. To count the tiles first, use the tile calculator.
How to use it
- Choose metric or imperial units and enter the “Tiled area”.
- Enter the “Tile length” and “Tile width”.
- Enter the “Joint width” (the spacer size) and the “Joint depth”, usually the tile thickness.
- Check the “Grout density” against your product's datasheet and set the “Extra for waste”.
- Enter the “Bag size” and read the grout weight and the bags to buy.
Worked example
A 12 m² floor of 600 × 300 mm tiles with 3 mm joints 10 mm deep. The joint factor is (600 + 300) ÷ (600 × 300) = 0.005 per mm, so grout per m² = 0.005 × 3 × 10 = 0.15 L. Over 12 m² that is 1.8 L, which at 1.6 kg/L weighs 2.88 kg. With 10% extra it is 3.168 kg: 0.63 of a 5 kg bag, so one bag.
Updated
Questions people ask
How do I work out how much grout I need?
Multiply the area by (tile length + tile width) ÷ (tile length × tile width), then by the joint width and the joint depth. In millimetres and square metres the answer is in litres; multiply by the grout's density for the weight.
What density should I use for grout?
Use the figure in the consumption formula on your grout's datasheet. It differs between products and between cement and epoxy grouts, so the default of 1.6 kg/L is only a starting point to replace with your own.
Why do small tiles need so much more grout?
Smaller tiles mean more joints per square metre. A 100 mm mosaic has six times the joint length of a 600 mm tile over the same area, so with the same joint size it needs about six times the grout.
Is the joint depth the same as the tile thickness?
Usually close to it, because grout fills the joint from the adhesive bed to the tile face. If adhesive squeezes up into the joints, or you rake them out shallower, enter the depth the grout will really fill.
How accurate is a grout estimate?
It is a planning figure. Uneven tile edges, hand-made tiles, porous surfaces and cleaning off all use more, and the formula slightly overstates very wide joints. Buy from one batch so the colour matches, and check the maker's coverage chart.