To find concrete materials, multiply the wet volume by 1.54 to get the dry volume, then split that dry volume by the mix ratio. For M20 (1:1.5:3), one cubic metre of concrete needs about 8.07 bags of cement (≈ 403 kg), 0.42 m³ of sand and 0.84 m³ of aggregate. Cement is counted in 50 kg bags, where one bag occupies 0.0347 m³.
Key takeaways
- Dry volume = wet × 1.54 for nominal mixes.
- 1 cement bag = 50 kg = 0.0347 m³ = 1.226 CFT.
- M20 (1:1.5:3): ≈ 8.07 bags / m³ of concrete.
- Cement share = dry vol × (1 ÷ sum of ratio parts).
- Sand ≈ 1,550 kg/m³, 20 mm aggregate ≈ 1,450 kg/m³.
How concrete quantities are calculated
Pick the grade and the tool reads its volumetric ratio (cement : sand : aggregate). It converts your wet volume to dry volume, splits the dry volume by the ratio parts, then turns the cement share into 50 kg bags.
Tonnes are found by multiplying each volume by its bulk density (sand 1,550 kg/m³, aggregate 1,450 kg/m³), and CFT by multiplying m³ by 35.3147.
Worked example: 1 m³ of M20 footing concrete
Say you are casting a column footing that needs 1 m³ of M20 (1:1.5:3) concrete. Dry volume = 1 × 1.54 = 1.54 m³. The ratio sums to 1 + 1.5 + 3 = 5.5 parts. Cement volume = 1.54 × (1 ÷ 5.5) = 0.28 m³, so bags = 0.28 ÷ 0.0347 ≈ 8.07 bags (about 403 kg). Sand = 1.54 × (1.5 ÷ 5.5) = 0.42 m³ (≈ 0.65 tonne), and aggregate = 1.54 × (3 ÷ 5.5) = 0.84 m³ (≈ 1.22 tonne). Add 5–10% for wastage before ordering.
Nominal mix ratios and cement per m³
| Grade | Mix (C:S:A) | Strength (N/mm²) | Cement bags / m³ | Typical use |
|---|---|---|---|---|
| M5 | 1 : 5 : 10 | 5 | 2.77 | Levelling / PCC base |
| M7.5 | 1 : 4 : 8 | 7.5 | 3.42 | Mass concrete |
| M10 | 1 : 3 : 6 | 10 | 4.44 | PCC, flooring base |
| M15 | 1 : 2 : 4 | 15 | 6.34 | Plinth, PCC |
| M20 | 1 : 1.5 : 3 | 20 | 8.07 | Slabs, columns (residential) |
| M25 | 1 : 1 : 2 | 25 | 11.09 | RCC (design mix preferred) |
Bag figures are for 1 m³ of wet concrete using the 1.54 factor and 0.0347 m³ per 50 kg bag.
Where this fits in your build
Use this for footings, columns, beams and small slabs. For a full slab, the RCC slab calculator adds a steel estimate; for the reinforcement weight itself, see the steel weight calculator. Sizing the plot first? Convert units with the land area converter.
Frequently asked questions
How many cement bags are in 1 m³ of M20 concrete?
About 8.07 bags. Wet × 1.54 = 1.54 m³ dry; cement share = 1 ÷ 5.5 = 0.28 m³; ÷ 0.0347 ≈ 8.07 bags (≈ 403 kg).
Why multiply wet volume by 1.54?
Dry materials have voids and bulk up; the standard nominal-mix factor is 1.54, so you need 1.54 m³ of dry material per 1 m³ of finished concrete.
What does the mix ratio 1:1.5:3 mean?
Parts by volume of cement : sand : aggregate. 1:1.5:3 is the nominal mix for M20 grade.
How do I convert sand and aggregate to tonnes?
Multiply m³ by bulk density — sand ≈ 1,550 kg/m³, 20 mm aggregate ≈ 1,450 kg/m³. So 1 m³ sand ≈ 1.55 t, 1 m³ aggregate ≈ 1.45 t.
What is the difference between M20 and M25?
The number is the 28-day strength in N/mm². M20 (1:1.5:3) suits residential slabs; M25 (1:1:2) is richer and usually a design mix.
Is this accurate enough to order materials?
It is a sound nominal-mix estimate. Add 5–10% wastage and confirm structural/design mixes with your engineer.
Method follows standard nominal-mix proportioning used in Pakistani practice (the common site standard for plain and reinforced concrete). The 1.54 dry-volume factor, 50 kg / 0.0347 m³ cement bag, and bulk densities (sand ≈ 1,550 kg/m³, aggregate ≈ 1,450 kg/m³) are standard trade values.
Last reviewed 2026-06-14