Concrete Mix Ratios Explained: 1:2:3, 1:2:4 and Water–Cement Ratio

Concrete is a mixture of cement, sand (fine aggregate), gravel (coarse aggregate) and water. Premixed bags and ready-mix trucks take the guesswork out, but if you mix your own from raw materials, or want to understand what you are ordering, mix ratios are where to start.

Reading a mix ratio

A ratio such as 1:2:3 means 1 part cement, 2 parts sand and 3 parts gravel, by volume, with enough water to make it workable. The parts can be shovels, buckets or wheelbarrows, as long as you use the same measure for each. The ratio is a proportion like any other; the ratio calculator scales it to any batch size.

Common ratios

Ratio (cement:sand:gravel)	Approx. strength	Typical use
1:3:6	Low	Mass fill, blinding layers
1:2:4	About 2,500–3,000 psi	General footings and slabs
1:2:3	About 3,000–3,500 psi	Slabs, patios, driveways
1:1.5:3	Higher	Structural members, heavy-duty slabs

Strengths are approximate because they depend heavily on the water content, materials and curing. Hand-mixed concrete rarely matches the consistency of plant-batched concrete, so treat home mixes as suitable for non-structural work.

The water–cement ratio

The most important number in concrete is not on the bag: it's the ratio of water to cement by weight. Less water makes stronger, more durable concrete; more water makes it easier to place but weaker and more prone to shrinkage cracks. Typical water–cement ratios range from about 0.40 to 0.60. For exterior concrete exposed to freezing, the lower end of that range is common.

As a rule, add water a little at a time until the mix holds its shape when you form it with a shovel and the surface glistens slightly without being soupy.

How much material for a cubic yard?

Because sand fills the spaces between gravel and cement fills the spaces in the sand, the dry ingredients add up to more than a cubic yard by bulk volume. A commonly used estimate for a 1:2:3 mix producing one cubic yard of concrete is roughly:

• Portland cement: about 6 bags of 94 lb (one bag is about 1 cubic foot)
• Sand: about 12 cubic feet
• Gravel: about 18 cubic feet
• Water: roughly 30–35 gallons, adjusted for the moisture already in the sand

Treat these as starting points and test a small batch. To find how many yards your project needs, use the concrete calculator; for buying sand and gravel by the ton, the gravel calculator converts volume to weight.

Mixing by hand

1. Measure the dry materials into a wheelbarrow or onto a mixing board.
2. Mix them dry until the color is uniform.
3. Make a hollow in the center, add part of the water and fold the dry material in.
4. Add the remaining water gradually until the mix is workable.
5. Place it within about an hour and protect it as it cures; see concrete curing time.

Safety

Cement dust irritates lungs and eyes, and wet cement is alkaline enough to cause chemical burns. Wear a dust mask when handling dry cement, plus gloves, eye protection and long sleeves. Wash skin promptly if it contacts wet concrete.

When to buy instead

For anything structural, or any pour over about a cubic yard, plant-batched ready-mix concrete is more consistent and usually more economical. For small non-structural jobs, premixed bags are simpler than sourcing three separate materials; see how many bags of concrete.