Mortar mix calculator
Mortar is specified as a volume ratio. The sand fills the voids, so the batch is smaller than the sum of its parts.
%
Cement
180.0kg
- 25 kg cement bags
- 8
- Sand
- 800
- Sand volume
- 0.500
- Lime volume
- 0.0000
- Approximate water
- 90.0
Show the working
- Mortar needed = 0.5
- Cement parts = 1
- Sand parts = 4
- Lime parts = 0
- Dry material bulking = 25
- parts = 1 + 4 + 0 = 5
- dry_volume = 0.5 * (1 + 25/100) = 0.625
- cement_vol = 0.625 * 1 / 5 = 0.125
- Sand volume = 0.625 * 4 / 5 = 0.5
- Lime volume = 0.625 * 0 / 5 = 0
- Cement = 0.125 * 1440 = 180
- Sand = 0.5 * 1600 = 800
- 25 kg cement bags = ceil(180 / 25) = 8
- Approximate water = 180 * 0.5 = 90
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- dry volume = wet volume x (1 + bulking)
- each material = dry volume x its share of the parts
A 1:4 cement:sand mortar suits general brickwork. A 1:1:6 cement:lime:sand mix is more forgiving and better for older, softer masonry.
Water at half the cement weight is a starting point; adjust for workability, not for the number.