Cement, sand and aggregate calculator
Enter a volume or the size of a slab, or an area of plaster. Pick a nominal mix. The page shows 50 kg cement bags, sand, aggregate and water.
- Bags, sand, aggregate
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How to use it
- Choose a volume, a slab, or mortar and plaster.
- Pick a grade from M5 to M25, a custom ratio, or a mortar ratio.
- Read bags to buy, sand, aggregate and the water for the mix.
Dry volume, bags and tonnes
Wet concrete is multiplied by 1.54 to get the dry volume of cement, sand and aggregate. Mortar uses 1.33. Cement is taken at 1,440 kg per cubic metre, so a 50 kg bag is about 0.035 m³. Bags to buy are rounded up. Sand is counted at 1.60 tonnes per cubic metre and coarse aggregate at 1.55.
Nominal ratios: M5 is 1:5:10, M7.5 is 1:4:8, M10 is 1:3:6, M15 is 1:2:4, M20 is 1:1.5:3 and M25 is 1:1:2. A blank water-cement ratio uses the grade default, from 0.45 for M25 to 0.60 for M5. One cubic metre of M20 is about 403 kg of cement, 0.42 m³ of sand and 0.84 m³ of aggregate.
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Questions
How many bags of cement are in one cubic metre of M20?
About 8.06 bags, 403 kg, so you buy 9 bags of 50 kg, with 0.42 m³ of sand and 0.84 m³ of aggregate at 1:1.5:3 and a dry factor of 1.54.
What is the 1.54 factor?
Cement, sand and aggregate bulk up when they are dry. Multiplying the wet concrete volume by 1.54 estimates the dry materials. Mortar and plaster use 1.33.
Which mix should I pick?
M20 at 1:1.5:3 is a common nominal mix for small slabs. M15 at 1:2:4 is leaner. M25 and richer work is often a design mix from the plant; the 1:1:2 line is the nominal equivalent.
How do I measure plaster?
Choose mortar, enter the wall or ceiling area and the thickness in centimetres, and pick 1:4 or 1:6. Thickness for a metric entry is in centimetres.
Can I add waste?
Yes. The waste percent increases the wet volume before the materials are split. Leave it at 0 to see the net quantity.