How this calculator works
Coverage mode divides area including waste by the package coverage and rounds to whole bags. The two PremiumPlus references use the low ends of the current manufacturer coverage ranges for a 50 lb bag; verify the local product sheet. Custom-bed mode treats the installed mortar as a uniform layer and converts wet volume to dry powder using the entered mixed density and dry fraction. Those initial properties are illustrative. Select a trowel and product for the tile and substrate, then check actual mortar transfer rather than choosing solely by tile size.
Formula
Coverage method: bags = ceil(area x (1 + waste) / coverage per bag). Bed method: V = area x final thickness; dry powder = V x (1 + waste) x mixed density x dry fraction; bags = ceil(dry powder / bag mass).
Worked example
Ten square metres at a final 3 mm bed use 0.03 m3 mortar. At 1600 kg/m3 and 75% dry powder by mixed mass, this is 36 kg powder, requiring two 20 kg bags. At $25 per bag, the purchase is $50.
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Frequently asked questions
Is the finished bed half the notch size?
Not reliably. Trowel angle, notch pattern, ridge collapse, substrate flatness and back-troweling change usage. Use published coverage or a measured bed thickness.
Does coverage include back-troweling?
The cited manufacturer chart excludes extra mortar on tile backs. Add its measured usage or a separate allowance when needed.
Why are wet volume and wet mass hidden in coverage mode?
Package coverage alone establishes bags, not wet density or bed thickness. Those quantities require the custom-bed method and product properties.