Concrete Mix Ratio Calculator

Standard Concrete Mix Ratios and Their Strength

Concrete mix ratios express the proportions of cement, sand, and coarse aggregate by volume. Richer mixes (more cement relative to aggregate) produce stronger concrete but cost more per cubic yard. The **concrete mix ratio calculator** converts any standard ratio into the exact quantities of each ingredient you need for your project volume.

| Mix Ratio | Approx. Strength (psi) | Typical Application | Cement per cu yd | |---|---|---|---| | 1:1:2 | 5,000+ | Precast, heavy structural | ~10 bags | | 1:1.5:3 | 4,000 | Foundations, columns | ~8 bags | | 1:2:3 | 3,500 | Slabs, footings, general structural | ~7 bags | | 1:2:4 | 2,500 | Driveways, sidewalks, patios | ~5.5 bags | | 1:3:5 | 2,000 | Light-duty slabs, garden walls | ~4 bags | | 1:3:6 | 1,500 | Bedding, non-structural fill | ~3.5 bags | | 1:4:8 | 1,000 | Mass fill, large volume backfill | ~2.5 bags |

Strength values are approximate 28-day compressive strengths and depend on water-cement ratio, curing conditions, and aggregate quality. Source: ACI 211.1 and PCA guidelines.

Bag counts assume standard 94-lb bags of Portland cement and a yield factor of 0.67. Always buy 5 to 10% extra cement to account for spillage and variations in aggregate moisture content.

Why the Yield Factor Matters More Than You Think

If you measure out 1 cubic foot of cement, 2 cubic feet of sand, and 3 cubic feet of gravel, you do not get 6 cubic feet of concrete. You get roughly 4 cubic feet. The yield factor — typically 0.65 to 0.70 — accounts for the fact that smaller particles fill the voids between larger ones.

Sand grains nestle into the spaces between gravel pieces. Cement powder fills the remaining gaps between sand grains. Add water, and the paste coats every particle and fills whatever air voids remain. The result: your combined dry ingredients compact into significantly less volume than you might expect.

This calculator defaults to a yield factor of 0.67, which works well for most standard mixes with well-graded aggregate. If your aggregate is uniformly sized (all the same diameter), the yield factor drops toward 0.60 because the particles do not pack as efficiently. If you are using a blend of fine and coarse aggregate that is well graded across multiple sieve sizes, the yield factor can reach 0.72 to 0.75.

Getting the yield factor wrong by even 10% can mean running short mid-pour — a serious problem when you need to fill a footing form continuously. For any pour over 10 cubic feet, measure a test batch first: mix one full bag of cement with the proportional sand and aggregate, then measure the resulting volume. Divide the measured volume by the dry ingredient volume to get your actual yield factor.

Mixing Concrete on Site: The Right Sequence

1. **Measure dry ingredients by volume.** Use a 5-gallon bucket or a known container as your measuring unit. For a 1:2:3 mix, measure 1 bucket of cement, 2 buckets of sand, and 3 buckets of gravel. Consistency between batches matters more than exact precision — use the same bucket and fill it to the same level each time.

2. **Combine dry ingredients first.** Add the aggregate to the mixer, then the sand, then the cement. Run the mixer for 1 to 2 minutes until the dry blend is uniform in colour. If hand-mixing in a wheelbarrow, blend with a hoe until no streaks of cement are visible.

3. **Add water gradually.** Start with about two-thirds of the calculated water amount. Add the rest in small increments, mixing for 30 seconds between additions. The target consistency is a thick paste that holds its shape when squeezed but slumps under its own weight — a 3 to 4-inch slump for most residential work.

4. **Check workability before pouring.** The mix should slide off a shovel cleanly without sticking. If it is too stiff, add water in half-gallon increments. If too soupy, add small amounts of sand and cement in the original ratio. Every gallon of excess water per cubic yard reduces the 28-day strength by approximately 200 to 300 psi.

5. **Pour and consolidate immediately.** Site-mixed concrete begins setting within 30 to 60 minutes in warm weather. Work the concrete into forms, tap the sides to release air pockets, and screed the surface level. For the [concrete reinforcement calculator](/calculators/structural/concrete-reinforcement-calculator), place rebar or mesh before pouring and ensure minimum 1.5 inches of cover from any formed surface.

Water-Cement Ratio and Its Effect on Strength

The water-cement ratio (W/C) is the single most controllable factor affecting concrete strength. Understanding this relationship prevents the most common mistake in site-mixed concrete: adding too much water.

What is the water-cement ratio? It is the weight of water divided by the weight of cement in the mix. A W/C of 0.45 means 0.45 pounds of water for every pound of cement. Lower ratios produce stronger, more durable concrete because excess water creates capillary pores as it evaporates during curing. Those pores weaken the hardened paste.

What W/C ratio should I target? For structural elements (footings, slabs bearing loads, columns), use 0.40 to 0.45. For general flatwork (patios, sidewalks), 0.45 to 0.50 is adequate. For non-structural applications, 0.50 to 0.55 improves workability without consequence. Never exceed 0.60 — the resulting concrete is weak and porous.

Why does everyone add too much water? Because dry, stiff concrete is hard to work with. It does not pour easily, it resists screeding, and it takes more effort to consolidate into corners of forms. Adding water makes the mix flow — but it also destroys strength. A 4,000 psi mix at W/C 0.45 drops to 2,500 psi at W/C 0.65. Use a plasticiser admixture (available at home centres) to improve workability without adding water.

Does aggregate moisture affect my water calculation? Absolutely. Wet sand can carry 5 to 8% moisture by weight, which is free water entering the mix. On a rainy day, reduce added water by the estimated moisture in the sand. Squeeze a handful — if water drips out, the sand is carrying significant moisture that counts toward your W/C ratio.

Site-Mixed vs Ready-Mix vs Bagged: Choosing the Right Approach

The method you use to produce concrete depends on volume, quality requirements, and access to the pour location.

**Pre-bagged concrete** (Quikrete, Sakrete) is the simplest option. Each 60 or 80-lb bag contains pre-proportioned cement, sand, and aggregate — just add water. Convenient for small jobs: fence posts, mailbox bases, and patching. The drawback is cost: at $5 to $8 per 80-lb bag (March 2026 home centre prices), a single cubic foot costs roughly $8 to $13. A cubic yard from bags runs $220 to $350, compared to $130 to $170 delivered from a ready-mix plant.

**Site-mixed concrete** — what this calculator is designed for — lets you buy raw ingredients separately and blend them in a portable mixer or wheelbarrow. For volumes between 3 and 27 cubic feet, site-mixing often hits the sweet spot: cheaper than bags, no minimum order or short-load fee from a ready-mix supplier. You also control the mix ratio precisely, which matters for non-standard applications. The limitation: mixing is physical work, and quality depends on consistent proportioning and water control.

**Ready-mix concrete** arrives in a truck, fully mixed to specification. For anything over 1 cubic yard (27 cu ft), ready-mix is almost always the right choice. The concrete is batched by computerised systems, tested for quality, and delivered at the correct slump. Most plants have a 1-yard minimum with a short-load surcharge ($30 to $60) for orders under 3 yards. The truck needs access within 30 to 40 feet of the pour location — if your backyard footing is 150 feet from the street, you will need a concrete pump ($200 to $500 rental) or a lot of wheelbarrow runs.

For projects that involve [concrete slab weight](/calculators/structural/concrete-slab-weight-calculator) calculations — like elevated slabs where the supporting structure must handle the dead load — site-mixed concrete works just as well as ready-mix, provided you maintain consistent proportioning and proper curing.

Worked Examples