How many cement bags are needed per m³ of M20 concrete?

For M20 grade concrete (mix ratio 1:1.5:3), you need approximately 8.2 bags of 50 kg cement per cubic metre of concrete, along with 0.41 m³ of sand and 0.83 m³ of coarse aggregate. Always add 5% extra for wastage.

What is the difference between M15 and M20 concrete?

M15 concrete has a characteristic compressive strength of 15 N/mm² and uses a 1:2:4 mix ratio (cement:sand:aggregate), requiring about 6.3 bags per m³. M20 has a strength of 20 N/mm² with a 1:1.5:3 ratio needing 8.2 bags per m³. M20 is the minimum grade for reinforced concrete structural members like slabs and beams.

How much wastage should I allow for concrete?

A standard wastage allowance of 5% is recommended for most concrete work. For complex shapes, sloping formwork or site conditions where spilling is likely, allow 7–10%. This calculator defaults to 5% but you can adjust it freely.

Can I use this calculator for RCC columns?

Yes. Select the Column tab, choose rectangular or circular cross-section, enter the dimensions and height, then select M20 or M25 grade (the minimum recommended for RCC columns). The calculator gives you the exact volume and material quantities. Note that this calculates concrete volume only — reinforcement steel quantity is not included.

Concrete Calculator – Cement, Sand & Aggregate

Concrete Shape

Length (m)

Width (m)

Thickness (mm)

Column Cross-Section

Length (m)

Width (m)

Height (m)

Length (m)

Width (m)

Depth (m)

Length (m)

Width (m)

Depth (m)

Mix & Options

Mix Grade

Unit System

Wastage (%)

Price per 50 kg Bag (optional)

Gross Volume—

Volume with Wastage—

Cement Bags (50 kg)—

Sand—

Coarse Aggregate—

Total Volume: —

Add 5% for wastage. Mix ratios are by volume. Sand density ≈ 1600 kg/m³; aggregate density ≈ 1500 kg/m³.

What is Concrete Mix Ratio?

A concrete mix ratio defines the proportion of cement, sand (fine aggregate) and coarse aggregate used to produce concrete of a specified strength. In India, mix grades are designated by the letter M followed by the characteristic compressive strength in N/mm² at 28 days.

M10 (1:3:6) — Lean mix used for levelling courses, PCC under footings, and non-structural filling where low strength is acceptable.
M15 (1:2:4) — Plain Cement Concrete (PCC) for foundation beds, pathway slabs and mass concrete where reinforcement is not required.
M20 (1:1.5:3) — The minimum grade specified by IS 456 for reinforced concrete members such as slabs, beams, columns and footings. The most commonly used mix for residential construction.
M25 (1:1:2) — Used for heavy-duty structural elements, high-rise buildings, bridges and pre-stressed concrete where higher strength and durability are required.

The calculator uses standard IS 456 dry ingredient factors derived from the wet concrete volume, accounting for the bulking effect of aggregates (typically a 1.54 to 1.57 factor over wet volume).

How to Use This Concrete Calculator

Step 1 — Select shape: Choose Slab, Column, Beam or Footing from the shape tabs at the top.
Step 2 — Enter dimensions: Fill in the relevant length, width and depth or thickness fields. For columns you can choose rectangular or circular cross-section.
Step 3 — Choose mix grade: Select the appropriate grade (M20 for most structural work, M15 for PCC, M10 for levelling).
Step 4 — Set wastage and unit: Default wastage is 5%. Switch between metric and imperial as required. Optionally enter the price per bag to get a cement cost estimate.
Step 5 — Click Calculate: Results show gross volume, volume with wastage, cement bags, sand and aggregate quantities.

Frequently Asked Questions

For M20 grade concrete (mix ratio 1:1.5:3) you need approximately 8.2 bags of 50 kg cement per cubic metre of finished concrete. Along with this you will need 0.41 m³ of fine aggregate (sand) and 0.83 m³ of coarse aggregate. Always order at least 5% extra for unavoidable wastage.

M15 has a characteristic compressive strength of 15 N/mm² and a 1:2:4 mix, requiring about 6.3 cement bags per m³. M20 has a 20 N/mm² strength with a 1:1.5:3 mix needing 8.2 bags. IS 456 mandates M20 as the minimum grade for all RCC structural work — slabs, beams and columns. M15 is only permitted for plain cement concrete (PCC) applications.

The standard recommendation is 5% wastage for most concrete pours. This accounts for material lost during mixing, transport and placement. For complex formwork shapes, sloping surfaces or sites where spilling is more likely, increase this to 7–10%. The calculator lets you enter any value between 0 and 30%.

Yes. Click the Column tab, select rectangular or circular cross-section, enter the column dimensions and height, and choose M20 or M25 grade (both are common for RCC columns as per IS 456). The calculator returns the concrete volume and all material quantities. Note that this tool calculates concrete volume only — the weight and quantity of reinforcement steel bars are not included.