How this calculator works
A repeating tile module consists of one tile plus one joint in each direction. Subtract tile area from module area to obtain the joint fraction without double-counting crossing joints. Multiply that fraction by total surface area and joint depth. This is a continuous repeating-grid estimate; perimeter joints and small cut-tile layouts differ. Mixed density and dry powder fraction are user-specified product properties. Manufacturer coverage tables take precedence for profiled tiles and proprietary grouts.
Formula
Joint fraction = 1 - (tile length x tile width) / [(tile length + joint width) x (tile width + joint width)]; grout volume = surface area x joint fraction x joint depth; dry mass = volume x (1 + waste) x mixed density x dry fraction.
Worked example
For 1.21 m2, 100 x 100 mm tiles, 10 mm joints and 10 mm joint depth, the module fraction is 21/121. Joint volume is 0.0021 m3, or 2.1 L. At 2000 kg/m3 and 100% dry fraction, 4.2 kg requires five 1 kg bags.
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Frequently asked questions
Is joint depth always the full tile thickness?
No. Use the depth actually filled after bedding mortar and joint cleaning. Follow the grout product requirements.
Why ask for dry powder fraction?
Mixed grout contains water. The dry fraction translates its estimated wet mass into powder purchased in bags. Obtain the value from the product mix proportions.
Can I use this for epoxy grout?
The geometric volume is useful, but the dry-powder bag model may not apply. Use the manufacturer kit coverage for multi-part products.