How the mix is worked out
Four steps, all arithmetic. First, the wet volume: length times width times depth, with the depth in inches divided by 12 to get feet — 10 times 10 times 4 divided by 12 is 33.33 cubic feet, which is 1.23 cubic yards. Second, the dry volume: wet concrete is denser than its dry ingredients, because the sand fills the gaps between the gravel and the cement paste fills the gaps between the sand, so the dry volume is the wet volume times 1.54 — 33.33 times 1.54 is 51.33 cubic feet. Third, the split: a 1:2:4 mix has 7 parts, so cement is 51.33 divided by 7, which is 7.33 cubic feet; sand is 2 parts, which is 14.67 cubic feet; aggregate is 4 parts, which is 29.33 cubic feet. Fourth, the weights: cement weighs 94 lb per cubic foot, so 7.33 times 94 is 689.33 lb; sand weighs about 100 lb per cubic foot, so 14.67 times 100 is 1,466.67 lb; gravel weighs about 95 lb per cubic foot, so 29.33 times 95 is 2,786.67 lb. Bags round up, because you cannot buy part of a bag: 689.33 lb of cement at 94 lb a bag is 7.33 bags, so buy 8; 1,466.67 lb of sand at 50 lb a bag is 29.33 bags, so buy 30; 2,786.67 lb of aggregate at 60 lb a bag is 46.44 bags, so buy 47. Water is half the cement weight at a 0.50 water-cement ratio — 689.33 times 0.50 is 344.67 lb — and water weighs 8.34 lb a gallon, so that is 41.33 gallons, or 156.44 liters.
The mix-ratio reference table
The ratio is cement to sand to aggregate by volume. Richer mixes — more cement — are stronger and cost more; leaner mixes are cheaper and weaker. The strengths below are the usual nominal 28-day compressive strengths for the ratio at a 0.50 water-cement ratio; the real strength of your pour depends on the water-cement ratio, the aggregate, the mixing, and the curing, so treat them as a guide, not a guarantee.
| Mix ratio | Nominal strength | Typical use |
|---|
| 1:1:2 | ~4,500 psi | High-strength work — columns, beams, heavily loaded slabs |
| 1:1.5:3 | ~3,000 psi | Driveways, footings, structural slabs |
| 1:2:3 | ~3,000 psi | General purpose — slabs, paths, steps |
| 1:2:4 | ~2,500 psi | General purpose — patios, walkways, shed bases |
| 1:3:6 | ~1,500 psi | Low-strength work — mass concrete, foundations, bedding |
The worked example, line by line
Setup: 10 ft × 10 ft × 4 in slab, mix 1:2:4, water-cement ratio 0.50.
Line 1 — wet volume. 10 × 10 × (4 / 12) = 33.33 ft³, or 1.23 yd³.
Line 2 — dry volume. 33.33 × 1.54 = 51.33 ft³.
Line 3 — the split. 7 parts: cement 51.33 / 7 = 7.33 ft³; sand 51.33 × 2 / 7 = 14.67 ft³; aggregate 51.33 × 4 / 7 = 29.33 ft³.
Line 4 — the weights. Cement 7.33 × 94 = 689.33 lb; sand 14.67 × 100 = 1,466.67 lb; aggregate 29.33 × 95 = 2,786.67 lb.
Line 5 — the bags. Cement 689.33 / 94 = 7.33, buy 8 bags; sand 1,466.67 / 50 = 29.33, buy 30 bags; aggregate 2,786.67 / 60 = 46.44, buy 47 bags.
Line 6 — the water. 689.33 × 0.50 = 344.67 lb; 344.67 / 8.34 = 41.33 gallons, or 156.44 liters.
Every branch, checked
1:1.5:3 mix, same volume: 5.5 parts, so cement is 51.33 divided by 5.5, which is 9.33 cubic feet — 877.33 lb, or 9.33 bags, so buy 10 bags. Sand is 14.00 cubic feet, 1,400 lb, so buy 28 bags. Aggregate is 28.00 cubic feet, 2,660 lb, so buy 45 bags. Water is 877.33 times 0.50 divided by 8.34, which is 52.6 gallons. Richer mixes cost more cement and more water.
1:3:6 mix, same volume: 10 parts, so cement is 51.33 divided by 10, which is 5.13 cubic feet — 482.53 lb, or 5.13 bags, so buy 6 bags. Sand is 15.40 cubic feet, 1,540 lb, so buy 31 bags. Aggregate is 30.80 cubic feet, 2,926 lb, so buy 49 bags. Water is 28.93 gallons. Leaner mixes save cement but use more aggregate.
Custom 1:2:3 mix, same volume: 6 parts, so cement is 51.33 divided by 6, which is 8.56 cubic feet — 804.22 lb, or 8.56 bags, so buy 9 bags. Sand is 17.11 cubic feet, 1,711.11 lb, so buy 35 bags. Aggregate is 25.67 cubic feet, 2,438.33 lb, so buy 41 bags. Water is 48.21 gallons.
5 ft × 5 ft × 4 in, 1:2:4: wet volume is 5 times 5 times 4 divided by 12, which is 8.33 ft³, and dry volume is 12.83 ft³. Cement is 1.83 cubic feet, 172.33 lb, so buy 2 bags. Sand is 3.67 cubic feet, 366.67 lb, so buy 8 bags. Aggregate is 7.33 cubic feet, 696.67 lb, so buy 12 bags. Water is 10.33 gallons.
1 yd³ wet volume, 1:2:4: 1 cubic yard is 27 cubic feet, so dry volume is 27 times 1.54, which is 41.58 ft³. Cement is 5.94 cubic feet, 558.36 lb, so buy 6 bags. Sand is 11.88 cubic feet, 1,188 lb, so buy 24 bags. Aggregate is 23.76 cubic feet, 2,257.20 lb, so buy 38 bags. Water is 33.47 gallons.
The reverse: cement on hand
Start with the cement you have and work forward. Ten 94-lb bags is 940 lb of cement, and at 94 lb per cubic foot that is 10 cubic feet. At 1:2:4, cement is 1 part of 7, so the dry volume is 10 times 7, which is 70 cubic feet, and the wet volume is 70 divided by 1.54, which is 45.45 ft³ — 1.68 yd³. The sand is 2 parts, which is 20 cubic feet or 2,000 lb, and the aggregate is 4 parts, which is 40 cubic feet or 3,800 lb. The water is half the cement weight — 470 lb — which is 56.35 gallons. Enter your own bag count in the calculator and it works the same way at any ratio.
Densities and the 1.54 factor, stated plainly
The densities on this page are the standard published values used in Portland Cement Association and American Concrete Institute mix guidance: cement 94 lb per cubic foot — one 94-lb bag is exactly one cubic foot — sand about 100 lb per cubic foot, and gravel about 95 lb per cubic foot. Real sand and gravel vary with moisture and grading, so the weights are close, not exact: wet sand weighs more than dry sand, and the calculator does not adjust for it. The 1.54 dry-to-wet factor is the standard rule of thumb for site-mixed concrete: the dry ingredients occupy about 54% more volume than the wet mix they make, because the voids between the particles close up when water and cement paste fill them. Ready-mix suppliers use their own batch weights and do not need this factor — it applies to site mixing from bags and bulk ingredients, which is what this calculator is for.
Rounding convention, stated plainly: volumes are kept to two decimals — wet 33.33 ft³, dry 51.33 ft³ — and weights to two decimals, then rounded to cents of a pound. Bags always round up to the next whole bag, because a partial bag cannot be bought: 7.33 bags of cement means buy 8. Water is shown to two decimals in gallons and one decimal in liters.
Output · formula · meaning
| Output | Formula | What it means |
|---|
| Wet volume | 10 × 10 × (4 / 12) | 33.33 ft³ — 1.23 yd³. |
| Dry volume | 33.33 × 1.54 | 51.33 ft³ — the voids factor. |
| Cement bags | 689.33 / 94, round up | 8 bags — exact is 7.33 bags. |
| Cement weight | 7.33 ft³ × 94 | 689.33 lb. |
| Sand weight | 14.67 ft³ × 100 | 1,466.67 lb — 30 bags of 50 lb. |
| Aggregate weight | 29.33 ft³ × 95 | 2,786.67 lb — 47 bags of 60 lb. |
| Water | 689.33 × 0.50 / 8.34 | 41.33 gal — 156.44 liters. |
| 1:1.5:3 mix | 51.33 / 5.5 parts | 10 bags of cement, 877.33 lb — 52.6 gal water. |
| 1:3:6 mix | 51.33 / 10 parts | 6 bags of cement, 482.53 lb — 28.93 gal water. |
| Custom 1:2:3 | 51.33 / 6 parts | 9 bags of cement, 804.22 lb — 48.21 gal water. |
| 5 × 5 ft × 4 in | 5 × 5 × (4 / 12) | Wet 8.33 ft³, 2 bags of cement — 10.33 gal water. |
| 1 yd³ wet | 27 ft³ × 1.54 | Dry 41.58 ft³, 6 bags of cement — 33.47 gal water. |
| Reverse: 10 bags | 940 lb → 10 ft³ cement | 45.45 ft³ wet, 1.68 yd³ — 2,000 lb sand, 3,800 lb aggregate. |
Who uses this
- The patio DIYer: pours a 10 ft by 10 ft slab, 4 inches thick, and learns it needs 8 bags of cement, 30 bags of sand, 47 bags of aggregate, and 41.33 gallons of water — a complete shopping list from one calculation.
- The driveway builder: switches to a richer 1:1.5:3 mix and learns the same volume needs 10 bags of cement and 52.6 gallons of water — more cement for a surface that takes car traffic.
- The small-job pourer: pours a 5 ft by 5 ft pad and learns it is only 8.33 cubic feet wet — 2 bags of cement, 8 of sand, 12 of aggregate, and 10.33 gallons of water.
- The bag-counter: has 10 bags of cement in the garage and learns they mix 45.45 cubic feet — 1.68 cubic yards — of concrete at 1:2:4, needing 2,000 lb of sand and 3,800 lb of aggregate.
Accuracy & limitations
The math is exact for the numbers you enter: the wet volume is length times width times depth, or the direct volume you enter; the dry volume is the wet volume times 1.54; the split follows the ratio parts; the weights use cement 94, sand 100, and gravel 95 lb per cubic foot; the bags round up; the water is the cement weight times the water-cement ratio, divided by 8.34 lb per gallon. But the inputs carry the assumptions. The densities are the standard published values from Portland Cement Association and American Concrete Institute mix guidance, and real sand and gravel vary with moisture and grading — wet sand weighs more than dry sand, and the calculator does not adjust for it. The 1.54 factor is the standard rule of thumb for site-mixed concrete, not a measured value for your particular aggregate, so a small pour can come out a bag over or under. The ratio strengths in the reference table are nominal 28-day values at a 0.50 water-cement ratio — the real strength of your pour depends on the water-cement ratio, the aggregate, the mixing, and the curing, so do not use this calculator for structural work that needs an engineered mix. Add 5 to 10% extra material for spillage, uneven ground, and formwork that is not perfectly true — the calculator gives the exact theoretical amount, and real pours always use a little more. No studies or statistics are cited on this page beyond the standard densities and the 1.54 factor, because none are needed: every figure is arithmetic on the numbers you enter.
Cite this calculatorBright Side Kit. “Concrete Mix Calculator: Cement, Sand & Gravel by Ratio.” brightoolbox.com, 2026. Method: wet volume = length × width × depth (or direct volume, 1 yd³ = 27 ft³); dry volume = wet × 1.54; ingredients split by ratio parts; weights at cement 94, sand 100, gravel 95 lb/ft³ (Portland Cement Association / ACI mix guidance); bags round up — cement 94-lb, sand 50-lb, aggregate 60-lb; water = cement weight × water-cement ratio / 8.34 lb/gal. Default: 10 ft × 10 ft × 4 in, 1:2:4, w/c 0.50 → wet 33.33 ft³, dry 51.33 ft³, cement 7.33 ft³ = 689.33 lb = 8 bags, sand 14.67 ft³ = 1,466.67 lb = 30 bags, aggregate 29.33 ft³ = 2,786.67 lb = 47 bags, water 41.33 gal (156.44 L). Reverse: 10 bags of cement → 45.45 ft³ (1.68 yd³) wet concrete at 1:2:4.Bright Side Kit. "Concrete Mix Calculator: Cement, Sand & Gravel by Ratio" https://brightoolbox.com/concrete-mix-calculator/ Accessed October 24, 2026.
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