Concrete Mix Ratio Calculator
Mixing concrete yourself? Choose a mix ratio and enter your volume to get the cement, sand, aggregate and water you need — by weight, by volume, and in cement bags.
Floors, pads, patios, driveways — flat rectangular pours.
How the mix ratio calculation works
The formula
Dry materials lose volume when mixed and compacted, so dry volume is taken as ~1.54× the finished wet volume. That dry volume is split by the ratio's parts, then converted to weight using standard bulk densities. Water follows the chosen water-to-cement ratio.
- Dry volume = wet volume × 1.54.
- Each material's share = dry volume × (its parts ÷ total parts).
- Cement 1,440 kg/m³, sand 1,600 kg/m³, aggregate 1,500 kg/m³.
- Water (litres) ≈ cement weight × water-cement ratio.
Worked example
1 m³ of M20 concrete at a 1 : 1.5 : 3 ratio:
- Dry volume = 1 × 1.54 = 1.54 m³; parts total = 5.5.
- Cement = 1.54 × 1/5.5 = 0.28 m³ ≈ 403 kg ≈ 8 × 50 kg bags.
- Sand ≈ 0.42 m³; aggregate ≈ 0.84 m³; water ≈ 200 L.
≈ 8 bags cement, 0.42 m³ sand, 0.84 m³ aggregate, ~200 L water per m³.
Sizing, thickness & waste
Common nominal mixes
- 1:3:6 — M10, lean concrete / blinding.
- 1:2:4 — M15, general non-structural work.
- 1:1.5:3 — M20, slabs, footings, light structural.
- 1:1:2 — M25, columns and higher-strength work.
Important
Nominal volume ratios are for planning and small jobs. Structural concrete should use a designed mix (target strength, w/c ratio, admixtures) verified by trial mixes or a supplier. Results are planning estimates. Always confirm volumes, mix designs and structural details with your supplier or engineer before pouring.
What produces this much concrete?
Consistent ratios are hard to hit by hand at volume. Batching and mixing equipment keeps every load on-spec:
Small pour — mix on site
Under ~0.5 m³ (≈0.65 yd³) you can mix on site from bags. A portable mixer saves time over hand-mixing once you pass a few bags.
Medium pour — small mixer or ready-mix
From ~0.5–2 m³, a small or self-loading mixer keeps you independent of delivery schedules; otherwise order ready-mix.
Large pour — self-loading mixer or delivery
At 2–10 m³, compare ready-mix delivery against a self-loading mixer or mixer truck if you pour regularly.
On-site batching becomes economical
Above ~10 m³, repeated or remote pours usually cost less with on-site batching than per-load delivery. A mobile or compact plant sets up fast.
Continuous production — dedicated plant
Beyond ~50 m³ per job, a stationary or ready-mix plant delivers the throughput and consistency large projects need.
Frequently asked questions
What is the ratio for concrete mix?
A general-purpose mix is 1:2:4 (cement:sand:aggregate), giving roughly M15 strength. Structural work commonly uses 1:1.5:3 (M20). Choose your ratio above and the calculator returns the quantities for your volume.
How much cement, sand and aggregate do I need per cubic metre?
For a 1:1.5:3 (M20) mix, about 8 × 50 kg bags of cement, 0.42 m³ of sand and 0.84 m³ of aggregate per cubic metre, plus roughly 200 litres of water. Use the calculator for other ratios and volumes.
How much water do I add to concrete?
Water is set by the water-to-cement ratio — typically 0.45–0.6 by weight. Lower ratios give stronger, less workable concrete. The calculator estimates litres from the cement weight and the selected ratio.
How much extra concrete should I order for waste?
Add 5–10% to your calculated volume to cover spillage, uneven subgrade, and over-excavation. For small or irregular pours, 10% is safer because running short mid-pour creates a cold joint.
Can I use this for structural concrete?
Results are planning estimates. Always confirm volumes, mix designs and structural details with your supplier or engineer before pouring.