Concrete Mix Ratio Calculator (Sand, Gravel, Cement)

Volume ratios only — this is not an engineered mix design. Structural concrete needs a tested design with a controlled water-cement ratio, and the batch tables below are for small, non-structural jobs: paths, pads, post footings and repairs.

Last updated: 7 November 2026 · Report an error

Worked example: one cubic yard (27 ft³) of finished 1:2:3 concrete starts as about 41.6 ft³ of dry ingredients — dry materials bulk roughly 54% larger than the wet concrete they yield, and the calculator includes that 1.54 dry-volume factor. Split six ways, one part is 6.93 ft³: cement 6.93 ft³ = 6.93 94-lb bags (651 lb), sand 13.86 ft³ (0.51 yd³ ≈ 0.69 t), gravel 20.79 ft³ (0.77 yd³ ≈ 1.09 t). That is why the cement figure runs higher than the bare "divide 27 by 6" split — the bare split forgets the bulking, and batches mixed to it come up short.

Every preset ratio in the calculator, worked for exactly one cubic yard of finished concrete — the same figures the tool returns for a 27 ft³ target, including the dry-volume factor:

Read the table the way a yard order goes: cement by the bag, sand and gravel by the yard or ton. Note what changes across the rows — the stronger 1 : 1.5 : 3 mix buys its strength almost entirely with cement (7.56 bags against 5.20 for the lean mix), which is why "just add more cement" is the expensive way to fix a weak design, and why the lean 1 : 3 : 4 belongs in blinding and mass fill, not in anything that carries load or weather.

Worked scenario — a 10 × 10 ft slab, 4 inches thick. The pour is 33.33 ft³ (1.23 yd³). At 1 : 2 : 4 the calculator returns 7.33 bags of cement (689 lb) — buy 8 — plus sand 0.54 yd³ (0.73 t) and gravel 1.09 yd³ (1.54 t). Mixing that in a small drum mixer means about eight one-bag batches: at 1 : 2 : 3, one 94-lb bag (≈ 1 ft³ of loose cement) with 2 ft³ of sand and 3 ft³ of gravel yields roughly 3.9 ft³ of placed concrete, which is the natural batch size for post holes and small repairs.

The ratio on this page covers the dry parts only, but water is where site mixes are won and lost. A workable general-purpose mix lands around 0.45–0.6 parts water per part cement by weight — for a 94-lb bag, roughly 5 to 6.5 gallons. Every extra splash from the hose raises that ratio and lowers the finished strength and frost resistance; a soupy mix that pours like soup cures like it too. Add water in stages, stop as soon as the mix is workable, and never re-wet a batch that has started to stiffen — remix it dry or discard it. Damp sand also brings its own water to the batch, one more reason to add the last of the water slowly.

Anything structural — beams, foundations carrying a building, retaining structures. These need a designed mix with a specified strength and a controlled water-cement ratio, and often an engineer's sign-off.

Freeze–thaw exposure. Driveways, steps and exterior slabs in cold climates need air-entrained concrete; a site ratio cannot dose air-entraining admixture reliably. Order ready-mix for exposed flatwork where winters bite.

Thin or reinforced sections. Where steel is close to the surface, aggregate size and grading matter as much as the ratio — oversized stone honeycombs around rebar.

Large or continuous pours. Past a couple of cubic yards, mixer time and cold joints eat the savings; a ready-mix truck is usually cheaper than the bags, and the strength is guaranteed by the plant.

The jobs this calculator most often serves, pre-computed at the general-purpose 1:2:3 ratio with the standard 1.54 dry-volume factor:

Fractional bags are why small pours so often end up as ready-mix bags instead: the post hole's 0.40 of a bag is one 40 lb ready-mix bag's neighbourhood, with the ratio already in it. The ratio route earns its keep from the 4 × 4 pad upward, where separate materials start beating bagged convenience on price.