Maker Tools
Concrete Calculator
Volume and bags for slabs and post holes, from your bag’s own yield.
✓ Free
✓ No account
◉ Runs on this device
Maker Tools
Powering up the tool…
TOOL CONCRETE-CAL
What this tool does
About the concrete calculator
Slab and cylinder maths with allowance, no assumed bag size.
How to use it
- Pick slab or post-holes.
- Enter dimensions.
- Enter the yield from YOUR bag’s label.
- Read m³ with allowance and bag count.
Useful for
- Order for a shed base or path.
- Count bags for a run of fence posts.
- Sanity-check a quote’s volume.
Straight answers
Concrete Calculator FAQ
How many bags per post?
Depends on hole and bag: a 25cm × 60cm hole is ~0.03m³ ≈ 2–3 typical 25kg bags. Enter your real sizes; the cylinder maths is exact even when the digging isn’t.
Why the 10% allowance?
Ground is never tape-measure flat, spillage exists, and running short mid-pour creates a cold joint — the defect you cannot fix later. Over by a bag beats under by a barrow, every time.