Cement Bag Calculator
Total cement, exact bags and whole bags to order.
Inputs
Result
Formula
| Total cement | volume × cement per m³ |
| With waste | total × (1 + waste%) |
| Exact bags | with waste ÷ bag weight |
| Whole bags | ceil(exact bags) |
| Surplus | bags × weight − with waste |
| Tonnes | with waste ÷ 1000 |
1 m³ of C25 at 320 kg/m³ with 50 kg bags and 3% waste: 320.0 kg of cement, 329.6 kg with waste, 6.59 bags exactly — order 7 for a 20.4 kg surplus.
FAQ
Why 3% for cement waste?
Bagged cement loses 1-3% in opening, tipping and mixer residue, while silo discharge loses 0.5-1%. Admixtures and fly ash follow the same logic. Three percent is the norm; on small jobs with hand mixing and few bags, 5% is safer because waste scales differently between 20 bags and 200.
Can damp, caked cement still be used?
Lightly caked cement that crumbles to powder can be screened and used at a lower grade after strength testing; lumps that will not crush have already hydrated with over 20% strength loss and must be scrapped. Beyond three months in store, strength drops 10-20%, and after six months it must be retested. Store it covered, off the ground, 300 mm clear of walls and no more than ten bags high.
Why not simply add more cement?
Because more cement is not more strength. Excess cement raises heat of hydration, increases shrinkage and cracking, and reduces durability. Strength comes from a low water-binder ratio, not from extra cement. Codes set both a minimum, for durability, and an effective upper limit, for heat — C30 usually sits between 320 and 400 kg/m³.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.