Cement Bag Calculator
Calculate the number of cement bags required for your concrete mix based on volume and mix ratio
Enter custom ratio — Cement : Sand : Aggregate (by volume)
Results
Step-by-Step Calculation
Understanding Concrete Mix Ratios
A concrete mix ratio describes the proportions of cement, sand (fine aggregate), and gravel/stone (coarse aggregate) by volume. The ratio determines the strength and workability of the final concrete. Water is added separately and typically ranges from 40-60% of the cement weight.
How Mix Ratios Work:
A ratio of 1:2:4 means for every 1 part cement, use 2 parts sand and 4 parts aggregate.
The total parts = 1 + 2 + 4 = 7 parts. Cement makes up 1/7 of the total dry volume. Due to voids between particles, the wet concrete volume is roughly 67% of the total dry volume of materials.
Cement Bag Sizes:
- 94 lb (42.6 kg): US standard bag — yields approximately 1 cubic foot of cement (0.035 m³)
- 50 kg (110 lb): International standard — yields approximately 1.18 cubic feet (0.033 m³)
- 80 lb (36.3 kg): Common retail size — yields approximately 0.60 ft³
- 60 lb (27.2 kg): Smaller retail size — yields approximately 0.45 ft³
- 40 lb (18.1 kg): Small project size — yields approximately 0.30 ft³
Mix Ratio Selection Guide
| Mix Ratio | Grade | Strength (psi) | Common Applications |
|---|---|---|---|
| 1:4:8 | M7.5 | ~1,090 | Leveling, mass concrete fill, non-structural |
| 1:3:6 | M10 | ~1,450 | Foundation base, garden walls, lean concrete |
| 1:2:4 | M15 | ~2,175 | General purpose — slabs, sidewalks, patios |
| 1:1.5:3 | M20 | ~2,900 | Structural — beams, columns, driveways |
| 1:1:2 | M25 | ~3,625 | High-strength — heavy loads, water tanks |
| 1:2:3 | — | ~2,500 | Moderate strength — floors, footings |
Tip: The two most common mix ratios for residential projects are 1:2:4 (general purpose) and 1:1.5:3 (structural). When in doubt, consult a structural engineer or local building codes.
Tips for Buying and Mixing Cement
Buying Cement
- • Check the manufacture date — use within 3 months
- • Store bags off the ground on pallets
- • Keep bags dry and covered
- • Avoid lumpy or hardened cement
- • Buy from reputable suppliers
- • Always round up to the nearest whole bag
Mixing Tips
- • Mix dry ingredients thoroughly before adding water
- • Add water gradually — avoid excess water
- • Water-to-cement ratio: 0.40 to 0.60 by weight
- • Mix until uniform consistency, no dry pockets
- • Use within 30-45 minutes of mixing
- • Use a mechanical mixer for large batches
Sand Quality
- • Use clean, sharp sand (not beach sand)
- • Free from clay, silt, and organic matter
- • Well-graded particle sizes for best results
- • River sand or manufactured sand recommended
Aggregate Quality
- • Use clean, hard, durable stone or gravel
- • Maximum aggregate size ≤ 1/3 of slab thickness
- • Typical sizes: 3/8", 1/2", 3/4", 1"
- • Free from clay coatings and debris
Bags vs. Ready-Mix: When to Use Which
Bagged Cement Mix
Best for:
- • Small projects (under 0.5 yd³)
- • Fence posts and mailbox posts
- • Small repairs and patches
- • Projects with limited access
- • DIY projects at your own pace
Ready-Mix Concrete
Best for:
- • Large projects (over 1 yd³)
- • Driveways, patios, foundation slabs
- • Structural elements needing consistent strength
- • Time-critical pours
- • Projects requiring specific mix designs
Related Calculators
Note: This calculator provides estimates based on standard concrete mix ratios and cement densities. Actual quantities may vary based on cement brand, aggregate moisture content, compaction, and site conditions. The 67% yield factor (dry volume to wet concrete volume) is an industry standard approximation. Always purchase a few extra bags to account for spillage, waste, and variations. For structural projects, consult a professional engineer for exact specifications.
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