# Cement Bag Calculator

Total cement, exact bags and whole bags to order.

- Page: https://jianzhujisuan.com/en/cement-bag
- Category: Material weights (https://jianzhujisuan.com/en/c/material-weight)
- Chinese version: https://jianzhujisuan.com/zh/cement-bag.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Volume 1 m³, Cement per m³ 320 kg/m³, Bag weight 50 kg, Waste allowance 3%): **Whole bags to order 7 bags**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Volume | number | 1 | m³ |  |
| Cement per m³ | number | 320 | kg/m³ | C25 about 320, C30 about 377, M10 mortar 300 |
| Bag weight | number | 50 | kg | 50 kg standard, 25 kg small bags also sold |
| Waste allowance | number | 3 | % |  |

## 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

## Worked example

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.

## Questions

### 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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