Cement Calculator

Cement Calculator works out how many bags of cement, and how much sand, coarse aggregate and mixing water, a site-batched nominal mix will take. Enter the size of the pour, pick the mix ratio and read the bags to order straight away. It works completely offline and nothing you enter ever leaves your phone.

HOW IT WORKS
The app uses the standard site "dry volume" method:

1. It measures the wet volume of the finished work from the length, width and thickness you enter — the volume the compacted concrete or mortar will occupy.

2. Your wastage allowance is added on top, for spillage and over-excavation.

3. Loose cement, sand and stone are full of air. Once water is added and the mix is placed and compacted, the fine particles drop into the voids and the batch shrinks. Multiplying by the dry volume factor — about 1.54 for concrete, about 1.33 for cement mortar — gives back the loose dry volume you actually have to buy.

4. The dry volume is split by the parts in the mix ratio. A mix written 1:1.5:3 means one part cement to one and a half parts sand to three parts coarse aggregate, 5.5 parts in all, so cement takes 1 / 5.5 of the dry volume.

5. The cement share is converted to mass at 1440 kg per cubic metre and divided by 50 kg for bags, rounded up. Sand is taken at 1600 kg per cubic metre and coarse aggregate at 1500. The mixing water is the cement mass times the water-cement ratio.

For a 4 m by 3 m slab 150 mm thick in M20 (1:1.5:3) with 5 percent wastage, that is 1.800 cubic metres wet, 2.911 cubic metres dry, 0.529 cubic metres of cement — 762 kg, so 16 bags — plus 0.794 cubic metres of sand, 1.588 cubic metres of aggregate and 381 litres of water at a water-cement ratio of 0.50.

WHAT YOU CAN DO
- Enter length, width and thickness and read the cement bags to order instantly
- Choose from the standard nominal mixes: 1:5:10, 1:4:8, 1:3:6 (M10), 1:2:4 (M15), 1:1.5:3 (M20) and 1:1:2 (M25)
- Switch to masonry mortar ratios of 1:3, 1:4, 1:5 and 1:6, which apply the mortar dry factor automatically
- Set the water-cement ratio from 0.35 to 0.70 and a wastage allowance from 0 to 20 percent
- See sand and aggregate in cubic metres, in cubic feet and by mass
- Open Details for a step-by-step breakdown, the assumptions applied and a table of cement bags per cubic metre for every standard mix
- Learn what the dry volume factor, the parts and the water-cement ratio actually mean, in plain language

BUILT FOR CLARITY
A kiln-violet, cement-inspired design puts the bag count first, with sand, aggregate, water and dry volume right beside it. Light and dark themes, a tiny download, no clutter and no account required.

AN ESTIMATE, NOT A MIX DESIGN
This is a simplified educational tool for volume-batched nominal mixes. Real quantities vary with aggregate grading and moisture, sand bulking, compaction, batching method, admixtures and cement type, and the 1.52 to 1.57 dry volume factor is a site rule of thumb rather than a design standard. Structural concrete should follow a mix design from your engineer or ready-mix supplier. Always confirm the final quantities with your supplier before ordering. This app is for general information and education only and is not professional construction advice.

PRIVACY
The app collects no personal data and works fully offline. Ads are served by Google AdMob, which may use an advertising identifier as described in Google's policies.

Download Cement Calculator and get a quick, sensible picture of the cement, sand, stone and water your next mix will take.