Concrete Mix Calculator
Estimates materials only, not a tested mix design. Follow your plans and local code for structural work. Wet cement burns skin, so wear gloves and eye protection.
A cubic yard of 4000 psi concrete, roughly a 1:2:3 mix, takes about 6.5 of the 94 lb bags of cement, plus about 14.5 ft³ of sand, 16 ft³ of gravel, and up to 34 gallons of water. A 3000 psi mix takes about 5.5 bags. Choose your mix and volume below. If your project requires a set strength, follow your plans.
Concrete mix ratios per cubic yard
| Mix | Typical strength | 94 lb bags per yd³ | 50 kg bags per m³ | Sand | Gravel | Water | Typical use |
|---|---|---|---|---|---|---|---|
| About 1:2:3 | 4000 psi | 6.5 | 7.2 | 14.5 ft³ | 16 ft³ | 34 gal | Foundations, reinforced slabs |
| 1:2.5:3 | 3500 psi | 6.4 | 7.1 | 16 ft³ | 19.2 ft³ | 35 gal | Garage floors, sidewalks |
| 1:3:3 | 3000 psi | 5.5 | 6.1 | 15.6 ft³ | 16 ft³ | 33 gal | Driveways, patios, walkways |
| 1:3:4 | 2500–3000 psi | 5.2 | 5.8 | 15.6 ft³ | 20.8 ft³ | 35 gal | Non-load-bearing work |
| 1:4:6 | 2000–2500 psi | 3.8 | 4.2 | 15.1 ft³ | 22.7 ft³ | 35 gal | Leveling and base layers |
How much cement, sand, and gravel do you need?
It depends on the mix. Published per-yard quantities put a 4000 psi mix at 611 lb of cement, 1,450 lb of sand, 1,600 lb of stone, and 33 to 35 gallons of water. A 3000 psi mix (1:3:3) uses 517 lb of cement, 1,560 lb of sand, 1,600 lb of stone, and 32 to 34 gallons. With 94 lb bags, that's about 6.5 and 5.5 bags per yard.
For a 6 × 6 ft slab, 4 in thick, the volume is 12 ft³, or 13.2 ft³ with 10% extra. A 4000 psi mix takes 4 bags of cement, about 7.1 ft³ of sand, 7.8 ft³ of gravel, and up to 16.6 gallons of water. In a mixer with a 3 ft³ batch, that's 5 batches.
Mix one bag at a time
On site, it's easiest to work per bag. For the 4000 psi mix, each 94 lb bag goes with about 2.2 ft³ of sand, 2.5 ft³ of gravel, and up to 5.2 gallons of water. Measure with the same container for every ingredient so the ratio holds. The result boxes show these amounts for whichever mix you choose.
What the mix ratios mean
A ratio like 1:2:3 means parts by volume: cement, sand, then gravel. The strengths in the table are typical published values. Ratios by volume are a rough guide and don't guarantee a strength, because the moisture in the sand, the aggregate size, and the water all change the result.
Why the numbers differ between sources
You'll see anywhere from 5.5 to 7 bags per yard quoted for a "standard" mix, and most of that is down to method. The 5.5 bags is a published figure for 3000 psi. Rows marked as volume ratios use a common shortcut: loose materials shrink when mixed, so you start with about 1.54 ft³ of dry material for each ft³ of concrete. With that factor, a true 1:2:3 comes to almost 7 bags, a little more than the published 4000 psi quantity. Bags of 50 kg or 42.5 kg change the count, so pick your size above.
Water is the part to control
The calculator shows up to about 34 gallons per yard, which is roughly 5.2 gallons per bag for the 4000 psi mix. Treat it as a ceiling. A lower water-cement ratio gives stronger concrete, so add water gradually and stop as soon as the mix holds together. Wet sand brings its own water, so you'll need less.
When site-mixed concrete isn't enough
These amounts are for estimating, not for certifying a structure. If your plans or inspector call for a set strength, a mix you measure by the shovel can't prove it. For foundations, retaining walls, and other structural work, follow your plans and local code, and consider ready-mix, which comes with a documented mix. To work out the volume for those jobs, see the footing calculator and concrete calculator.
How to mix concrete
- Measure. Use one bucket for all the ingredients and keep each scoop level. Sand and gravel should be clean and free of soil.
- Start the mixer. Add some of the gravel and water first, then the cement and sand, and finally the rest of the gravel.
- Adjust the water. Add the rest slowly until the mix is workable, then let it run for a few more minutes.
- Place and consolidate. Work quickly, rod the concrete to remove air, and strike it off. Don't add water to concrete that has started to stiffen.
- Cure it. Keep it damp and covered so it doesn't dry too fast, and don't pour on frozen ground.
Mixing your own or buying premixed?
Premixed bags are simplest for small jobs, since the blend is already right. An 80 lb bag yields 0.60 ft³, so a cubic yard takes 45 bags. Mixing from scratch can pay off when you can get sand and gravel delivered at a good price and have several batches to do. Enter your prices above, with sand and gravel per short ton, and compare the total with bags or a ready-mix quote. Keep the labor in mind too: a yard is about 3,700 lb of dry material to move by hand.
Common mistakes
- Too much water. It makes concrete easier to place but weaker when it cures.
- Switching containers. A ratio only holds if the same bucket and level scoops are used throughout.
- Using only sand. Sand and cement make mortar. Concrete needs gravel for strength and volume.
- Ignoring wet sand. It brings water with it and weighs more, so cut the added water.
- Relying on a ratio for structural work. Follow the plans for footings, walls, and anything else carrying a load.
Recipes and strengths come from the sources listed below, and the example quantities come from this calculator. Neither replaces testing. Sand and gravel volumes assume 100 lb/ft³ loose.
Frequently asked questions
How many bags of cement are in a yard of concrete?
About 6.5 of the 94 lb bags for a 4000 psi mix (roughly 1:2:3) and 5.5 for a 3000 psi mix (1:3:3). Lean mixes use fewer. Add your waste allowance on top, since you can only buy whole bags.
What is the mix ratio for concrete?
A common all-purpose ratio is 1:2:3 by volume: one part cement, two parts sand, and three parts gravel. It is typically quoted at around 4000 psi. A 1:3:3 mix is typically quoted at 3000 psi and suits driveways and patios. Ratios by volume are a rough guide, not a guarantee.
How much sand and gravel do I need per bag of cement?
For the 4000 psi mix, a 94 lb bag goes with about 2.2 ft³ of sand and 2.5 ft³ of gravel, plus up to about 5.2 gallons of water. The calculator shows the per-bag amounts for each mix.
How much water goes in concrete?
Up to about 34 gallons per cubic yard for a workable mix. Add it gradually and stop when the mix holds together, because extra water weakens concrete. A lower water-cement ratio gives stronger concrete, and wet sand already brings water with it.
What is the dry-volume factor of 1.54?
Loose materials shrink when they are mixed and wet, so you need about 1.54 ft³ of dry material per ft³ of concrete. The calculator uses it for volume ratios such as 1:3:4. It runs a little higher than the published per-yard quantities, which leaves you a small margin.
Why do sources disagree on bags per yard?
They use different mixes and methods. The published 5.5 bags is for a 3000 psi mix, while a true 1:2:3 by the 1.54 factor works out near 7 bags. The calculator labels which method each mix uses.
Is it cheaper to mix my own concrete?
Sometimes, if you can get sand and gravel delivered at a good price. Premixed 80 lb bags are simplest for small jobs, at about 45 bags per yard. Once you reach about a yard, price ready-mix too. Enter your local prices above to compare.
Can I mix my own concrete for a footing?
Check your local code and plans first. Small, non-structural footings are often mixed on site, but a required strength usually calls for a tested ready-mix or bagged product. This calculator estimates materials and does not certify a mix.
How much concrete fits in a mixer?
Check the rating for your mixer, because some list the drum size and not the batch size. Enter the batch size above and the calculator divides your total by it, rounding up.
What is f'c or psi?
Both describe compressive strength after curing, usually at 28 days. 3000 psi is about 210 kg/cm² or 21 MPa. A site-mixed batch only reaches its target with good materials, the right water, and proper curing, so treat these as typical values.
Related calculators
Sources
- Concrete Mixing RatiosEverything About ConcreteQuantities per cubic yard for 3000 and 4000 psi mixes, common ratios with typical strengths and uses, and the effect of the water-cement ratio.
- Beton-Misch-Rechner (in German)rechner-portal.deWater by consistency, volume ratios as a rough guide only, and mixer batch limits.
- Concrete Mix — product lineQUIKRETEBag yields used to compare mixing from scratch with premixed bags.