Concrete Bag Calculator
Shopping for bagged concrete instead of a ready-mix truck? Enter your concrete volume (m³) and the bags per m³ rate for your bag size, and the calculator returns the bag count rounded up to whole bags — the default rate of 67 matches a 30 kg bag.
Your result will appear here.
Concrete Bag Calculator online
Convert a concrete volume into the number of pre-mixed bags it takes — at the yield of the bag size you are buying — for small pours where a ready-mix truck does not make sense.
| Bag size | Yield per bag (m³) | Bags per m³ |
|---|---|---|
| 20 kg | 0.010 | 100 |
| 25 kg | 0.0125 | 80 |
| 30 kg | 0.015 | 67 |
| 60 lb | 0.45 ft³ | 79 |
| 80 lb | 0.6 ft³ | 59 |
How it works
The math is one line: Bags = round up(Volume × Bags per m³). The page always rounds up with a ceiling function, so 167.5 bags becomes 168 — you cannot buy half a bag. The default second field is 67, which is the rate for a 30 kg bag yielding about 0.015 m³ (1 ÷ 0.015 = 66.67, rounded to 67). Change that rate whenever you use a different bag size, using the reference table on the page.
Worked example
A garden slab 6 m long, 4 m wide and 0.15 m thick needs 6 × 4 × 0.15 = 3.6 m³ of concrete. At the default 30 kg rate: 3.6 × 67 = 241.2, rounded up to 242 bags. For a small footing 0.3 × 0.3 × 1.2 m = 0.108 m³ poured with 20 kg bags (100 per m³): 0.108 × 100 = 10.8, rounded up to 11 bags. At that scale — anything above roughly 2 m³, or about 134 bags at the 67 rate — compare the bag total against a ready-mix quote before buying.
Bag sizes
The reference table covers five options: 20 kg yields 0.010 m³ per bag, so 100 bags per m³; 25 kg yields 0.0125 m³, so 80 per m³; 30 kg yields 0.015 m³, so 67 per m³; 60 lb yields 0.45 ft³, so 79 per m³; 80 lb yields 0.6 ft³, so 59 per m³. Type the matching per-m³ number into the second field — for example 80 for 25 kg bags or 59 for 80 lb bags.
Practical tips
- Add waste to the volume first. This page has no waste field, so inflate the volume by 5–10% yourself (3.6 m³ becomes about 3.8–4.0 m³) before calculating.
- Trust the round-up. The ceiling already covers fractional bags; do not round down to save money.
- Keep one bag size per calculation. Mixed 20 kg and 30 kg bags need separate runs.
- Confirm volumes with drawings. The result is a planning estimate, not a mix design or structural approval.
Edge cases and limitations
- The rate is a yield, not a weight. Bags-per-m³ comes from how much placed concrete one bag makes (a 30 kg bag yields about 0.015 m³, hence 67 per m³). Brands differ by ±10% — the yield printed on your bag overrides any default here, so check it before ordering a pallet.
- Waste is not in the rate. The calculation covers the neat volume only. Spillage, over-dug footings and the heel left in the mixer are yours to add: inflate the volume by 5–10% before entering it.
- Pallets and water. Bags ship on pallets of roughly 40 × 30 kg (supplier-dependent) — a 242-bag job is about six pallets and needs a forklift plan, not a car boot. Each 30 kg bag also wants about 3 litres of mixing water; have it on site before the first bag opens.
- There is a crossover point. Beyond roughly 1–1.5 m³, bag mixing usually costs more in bags and labour than a small ready-mix load, even with a part-load charge. Price both before committing to hundreds of bags.
Privacy and browser processing
The calculation runs entirely in your browser — the dimensions you enter are never uploaded.
Frequently asked questions
How many 25 kg bags make one cubic metre?
80. Each 25 kg bag yields about 0.0125 m³, so 1 ÷ 0.0125 = 80. Enter 80 in the Bags per m³ field.
Why did 167.5 bags become 168?
The tool applies a ceiling function to every result, because suppliers sell whole bags. Any fraction — even 167.1 — rounds up to the next integer.
Does the calculator include a waste allowance?
No. It has only two inputs, volume and rate. Multiply your net volume by 1.05 to 1.10 for spillage and uneven subgrade, then enter the inflated volume.
How many 80 lb bags do I need per cubic metre?
59. An 80 lb bag yields about 0.6 ft³, and a cubic metre holds 35.31 ft³, so 35.31 ÷ 0.6 = 58.86, which the table rounds to 59.