Concrete volume and bags with 10% waste
Length×width×thickness in meters → m³. Add 10% waste for formwork and uneven ground. Divide by bag yield 25kg≈0.013m³ 40kg≈0.0208m³. This calculator is designed for quick, private, offline use in your browser. All formulas run locally and are verified against official sources. You enter the core numbers, see the result instantly, and can check the steps, so you avoid the common mistake of applying a percentage to the wrong base or mixing units. Keep the inputs in the same unit system, verify the rate or factor for your country, and compare the result with a second example to catch typos before you save or file. Concrete is sold by volume, not weight on site. Length × width × thickness in meters gives m³. Add 10% waste because formwork leaks, ground is uneven and you never scrape the last shovel clean. Divide
TL;DR
- Volume = L×W×thick/100 (cm→m).
- Formulas: Vol=L×W×thick/100 | Waste=Vol×1.10 | Bags=Vol/yield
- 4×5 10cm — 2.0m³
How it works
Volume = L×W×thick/100 (cm→m). Waste = Vol×1.10. Bags = Vol/wield ceil. 4×5×0.10 →2.0m³ 2.2m³ waste →170×25kg. Start with clean inputs, keep the same units, and follow the order the formula shows. The tool does the arithmetic, but you decide the rate, period, or factor. A second example with different numbers shows how the result scales, which is the fastest way to spot a misplaced decimal or a monthly versus annual confusion before you act on the number. Concrete is sold by volume, not weight on site. Length × width × thickness in meters gives m³. Add 10% waste because formwork leaks, ground is uneven
The math
2×2×0.15 →0.6m³ 0.66 waste →51×25kg. Always cm/100.
Cannot buy half bag, ceil. Mesh not in volume.
Examples
4×5 10cm
- 2.0m³
- 2.2 waste
- 170×25kg
2×2 15cm
- 0.6m³
- 51×25kg
When to use it
✦ Slab
Order concrete.
✦ DIY
Bags vs ready-mix.
⚠ Common mistakes
- cm not /100
- No waste → short
FAQ (6)
25kg bag?
0.013m³, 40kg 0.0208m³ varying.
Rebar?
Mesh needed >10cm, volume same.
Do you save the numbers I type for area, volume or conversions?
Not at all. Every conversion — kg to lbs, area, fraction math — runs locally. No form data is posted anywhere. You can convert 1,500 kg to lbs on a shared computer and walk away knowing nothing was logged.
Will it work without internet in class?
Yes — that's why students like it. Load once on Wi-Fi, then fraction, base-converter or standard deviation work offline in class or in an exam hall without signal. It's just math in JavaScript, no server round-trip.
How accurate are the math results?
We use standard definitions (e.g. 1 kg = 2.20462 lbs, BIPM SI) and double-check edge cases via automated tests. For homework or site measurements it's more than enough, but for certified engineering or lab work, cross-check with the primary standard.
Can I share a calculation with a classmate?
Tap 'Share Link' — it puts the inputs in the URL. Your classmate opens it and sees the same 3/4 → 0.75 → 75% breakdown instantly, without retyping.
Sources & References
How this calculator is maintained
This calculator is written and maintained by Davide Coronese, independent developer and founder of CalcTracker.
Methodology: every formula is checked against official publications and validated by an automated test suite before release. Health, tax and finance pages cite the exact sources they rely on.
Found an error? Contact us — verified corrections ship within 24 hours.