🏗️ Cement Calculator
Updated June 2026 · Cement ₹340-450/bag (OPC 50kg) · M20 is residential standard
For 100 cft of M20 concrete (the standard for residential slabs and foundations), you need 16 cement bags, 45 cft sand, and 90 cft aggregate — costing about ₹6,400 at ₹400/bag. Enter your concrete volume and grade below to get exact quantities.
Cement Estimate
The Cement Math (Worked for 100 cft of M20)
Here is the exact computation the calculator runs, using 100 cft of M20 concrete (1:1.5:3 mix) at ₹400/bag:
- Concrete volume: 100 cft (= 2.83 cubic meters)
- Grade factor: M20 = 8 (derived from the dry-to-wet volume ratio and mix proportions)
- Cement bags: ceil(100 × 8 ÷ 50) = 16 bags (50 kg each = 800 kg total)
- Sand: 100 × 0.45 = 45 cft
- Aggregate: 100 × 0.9 = 90 cft
- Cement cost: 16 × ₹400 = ₹6,400
Mix ratios per IS 456:2000 — M20 = 1:1.5:3 (cement:sand:aggregate by volume). The grade factor accounts for dry volume being 1.54× wet volume and the cement proportion in the mix. Sand and aggregate are approximate — exact quantities depend on moisture content and bulk density.
Cement Bags by Grade and Volume
How the cement bag count changes with concrete grade (higher grade = more cement):
| Volume | M10 (1:3:6) | M15 (1:2:4) | M20 (1:1.5:3) | M25 (1:1:2) |
|---|---|---|---|---|
| 50 cft | 6 bags | 7 bags | 8 bags | 10 bags |
| 100 cft | 11 bags | 13 bags | 16 bags | 19 bags |
| 200 cft | 22 bags | 26 bags | 32 bags | 38 bags |
| 500 cft | 55 bags | 65 bags | 80 bags | 95 bags |
The M20 row is highlighted because IS 456:2000 specifies M20 as the minimum grade for reinforced cement concrete (RCC) in residential construction. Using M15 for structural work is a code violation and a safety risk.
Which Grade Do You Need?
| Grade | Ratio | Strength | Used For |
|---|---|---|---|
| M10 | 1:3:6 | 10 MPa | Levelling course, PCC below foundation, non-structural fill |
| M15 | 1:2:4 | 15 MPa | Flooring, paving, non-structural walls |
| M20 | 1:1.5:3 | 20 MPa | Residential slabs, beams, columns, foundations (RCC minimum) |
| M25 | 1:1:2 | 25 MPa | Commercial buildings, heavy-load structures, high-rise columns |
Common Advice vs Reality: "Use M25 for Extra Strength"
Some contractors recommend M25 for residential construction "for extra safety." In practice, M20 meets IS 456:2000 requirements for all residential RCC work. Upgrading to M25 adds 20% more cement cost (19 bags vs 16 per 100 cft) with no meaningful safety benefit for a 2-3 storey home. The money is better spent on better steel reinforcement or a thicker slab. Use M25 only if your structural engineer specifies it for specific load-bearing elements.
The Common Mistake: Measuring Wet Volume Instead of Dry
When you order concrete materials, the volumes are dry. Dry sand and aggregate occupy more volume than wet (because of bulking). The calculator accounts for this by using the grade factor which includes the 1.54 dry-to-wet conversion. If you calculate 100 cft of wet concrete and order materials for exactly 100 cft without the conversion, you'll be short by about 35%.
Edge Case: Ready-Mix Concrete (RMC) vs Site Mix
For volumes above 150-200 cft, consider ready-mix concrete (RMC) instead of site mixing. RMC for M20 costs ₹5,200-7,000 per cubic meter (~₹1,470-1,980 per 100 cft), delivered by transit mixer. For 100 cft of M20, site mixing costs about ₹6,400 (cement) + ₹2,700 (sand) + ₹4,500 (aggregate) = ₹13,600, while RMC costs about ₹1,500-2,000. RMC is cheaper for large volumes, guarantees mix quality, and saves labour time. For small volumes (under 50 cft), site mixing is more practical.
Decision Framework: Choosing the Right Grade
- Foundation PCC (below RCC): M10 or M15. This is a levelling layer, not structural.
- Residential RCC (slab, beams, columns): M20. This is the IS 456 minimum and sufficient for 2-3 storey homes.
- Commercial or heavy-load: M25. Only if specified by a structural engineer.
- Flooring and paving: M15. Adequate for non-structural flatwork.
- Budget tip: Don't downgrade from M20 to M15 for structural elements to save cement — the ₹2,000 saved per 100 cft isn't worth the structural risk.
The 2-Minute Self-Check
- Calculate your concrete volume: length × width × thickness (all in feet) = cubic feet.
- For a 1000 sqft slab that's 4.5 inches thick: 1000 × 0.375 = 375 cft.
- Select M20 for RCC work (slabs, beams, columns) or M15 for non-structural.
- Enter your local cement price (₹340-450/bag depending on brand and city).
- Run the calculator and verify with your contractor — the numbers should be within 10% of each other.
Your Next Steps
- Run the cement calculator for each concrete element (foundation, slab, columns) separately.
- Calculate bricks for your walls at the Brick Calculator.
- Estimate steel reinforcement at the Steel Calculator.
- See total project cost at the House Cost Calculator.
- Check current cement prices in your city at our material prices page.
Frequently Asked Questions
How many cement bags do I need for 100 cft of M20 concrete?
You need about 16 bags of cement (50kg each), 45 cft of sand, and 90 cft of aggregate for 100 cft of M20 concrete. M20 uses a 1:1.5:3 mix ratio (cement:sand:aggregate).
What is the difference between M15 and M20 concrete?
M15 (1:2:4) has a compressive strength of 15 MPa and is used for non-structural work like flooring and paving. M20 (1:1.5:3) has 20 MPa strength and is the minimum grade for structural RCC work like slabs, beams, and columns per IS 456.
How much does a cement bag cost in India in 2026?
A 50kg bag of OPC cement costs ₹340-450 depending on brand (UltraTech, ACC, Ambuja, Shree) and region. PPC cement is slightly cheaper at ₹320-400 per bag.
Should I use ready-mix concrete or mix on site?
For volumes above 150-200 cft, ready-mix concrete (RMC) is cheaper and guarantees mix quality. For smaller volumes (under 50 cft), site mixing is more practical. RMC for M20 costs about ₹5,200-7,000 per cubic meter delivered.
Editor Note
Reviewed June 2026. Mix ratios per IS 456:2000. Cement bag count includes the 1.54 dry-to-wet volume conversion. Sand and aggregate quantities are approximate - actual consumption depends on moisture content and bulk density. For structural RCC, always use M20 minimum and consult a structural engineer. If you spot an outdated figure, please contact us.