Cement Calculator
Enter your slab, footing or column size, or a known concrete volume, and pick a mix ratio. You get the number of 94 lb, 50 kg or 25 kg cement bags to buy, plus the sand, coarse aggregate and water for a site-mixed batch.
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Cement = wet volume × 1.54 × cement part ÷ sum of the ratio × 1,440 kg/m³, divided by the bag weight. A 12 × 10 ft slab 4 in thick is 1.13 m³. With 5% waste and a 1:2:4 mix it needs 377 kg of cement, so buy 9 bags of 94 lb or 8 bags of 50 kg.
How to use this cement calculator
- Pick what you are pouring. A slab or footing, round columns, or a volume you already know.
- Enter the size. Thickness is in inches (or cm in metric). A typical patio or shed slab is 4 in.
- Choose the mix ratio from your drawings or the job: 1:2:4 for general work, 1:1.5:3 for slabs and beams.
- Choose your bag size. 94 lb is the standard US portland cement bag. 50 kg and 25 kg bags are common elsewhere.
- Read the order: cement bags and cost, then sand and coarse aggregate by volume and approximate weight.
How to calculate cement for concrete
The 1.54 dry volume factor covers the air gaps in loose materials that close up when the concrete is mixed. 1,440 kg/m³ is the standard bulk density used for cement, so a 50 kg bag holds about 0.0347 m³ (1.23 ft³) and a 94 lb bag about 1.05 ft³.
| Mix ratio | Typical grade | Cement per m³ | 50 kg bags per m³ | 94 lb bags per yd³ |
|---|---|---|---|---|
| 1 : 1 : 2 | about M25 | 554 kg | 11.1 | 9.9 |
| 1 : 1.5 : 3 | about M20 | 403 kg | 8.1 | 7.2 |
| 1 : 2 : 4 | about M15 | 317 kg | 6.3 | 5.7 |
| 1 : 3 : 6 | about M10 | 222 kg | 4.4 | 4.0 |
| 1 : 4 : 8 | M7.5 | 171 kg | 3.4 | 3.1 |
Figures are per unit of finished concrete with no waste. Nominal mixes are a rule of thumb. Where a strength is specified, follow the mix design from your engineer or supplier.
Cement, concrete mix or ready-mix?
- Portland cement (94 lb, 50 kg, 25 kg)Pure binder. You buy sand and gravel separately and mix on site. Cheapest per yard for larger site-mixed pours.
- Bagged concrete mix (60 or 80 lb)Cement, sand and gravel already blended. An 80 lb bag yields about 0.6 ft³, so it suits small jobs. Use the bags of concrete calculator for those.
- Ready-mix truckUsually the better choice above 1–2 yd³. Order by the cubic yard from the concrete yardage calculator.
Worked example
- Slab 12 × 10 ft, 4 in thick
- 40 ft³ = 1.48 yd³ = 1.13 m³
- Add 5% waste
- 1.19 m³ wet
- Dry volume (× 1.54)
- 1.83 m³
- Cement for 1:2:4 (1 part of 7)
- 1.83 ÷ 7 = 0.262 m³ × 1,440 = 377 kg
- Bags to buy
- 9 × 94 lb (≈ $144 at $16) or 8 × 50 kg
- Sand (2 parts) and aggregate (4 parts)
- 0.52 m³ (0.68 yd³) and 1.05 m³ (1.37 yd³)
Frequently asked questions
How do I calculate cement for concrete?
Wet volume × 1.54 for dry volume, ÷ the sum of the ratio, × the cement part. Multiply the cement volume in m³ by 1,440 kg/m³ and divide by the bag weight.
How many bags of cement are in 1 cubic meter of concrete?
About 6.3 bags of 50 kg for 1:2:4, 8.1 for 1:1.5:3 and 4.4 for 1:3:6, before waste.
How many 94 lb bags of cement per cubic yard?
About 5.7 for 1:2:4, 7.2 for 1:1.5:3 and 4 for 1:3:6, before waste.
Why multiply by 1.54 for dry volume?
Loose cement, sand and aggregate have air gaps that close when mixed, so you need more dry material than the finished volume. 1.54 is the common factor; some engineers use 1.52–1.57.
Is a 94 lb bag of cement the same as an 80 lb bag of concrete?
No. 94 lb is pure portland cement that you mix with sand and gravel. An 80 lb bag of concrete mix already contains them and yields only about 0.6 ft³.
How much water do I need for the cement?
At a 0.5 water-cement ratio, 0.5 liter per kg of cement: about 25 liters per 50 kg bag or 5.6 gallons per 94 lb bag. Wet sand needs less.
What this calculator assumes
- Nominal volume mixes with a dry volume factor of 1.54 (editable) and cement at 1,440 kg/m³.
- Sand and aggregate weights use typical loose dry densities of 1,600 and 1,550 kg/m³. Damp sand bulks up, so check with your supplier.
- Water is a rough guide at a 0.5 water-cement ratio. Follow your mix design where strength matters.
- Thickness, mix and any reinforcement must follow your plans and local building code. Prices are editable estimates before tax and delivery.