Concrete calculators & guides
Free concrete tools and plain-English guides for New Zealand — each gives the answer fast and shows the working behind it.
Concrete calculator
How much concrete do I need? Enter length, width and thickness — get cubic yards, metres and bags.
Open tool →Gravel calculator
How much gravel do I need? Enter length, width and depth — get tons, cubic yards and tonnes for gravel, road base or sand.
Open tool →Asphalt calculator
How much asphalt do I need? Enter length, width and thickness — get the tons (and tonnes) of hot-mix asphalt to order for a driveway, path or car park.
Open tool →About concrete calculations
Every concrete job starts with the same question — how much? — and punishes a wrong answer in a way few other materials do. Order short and the pour stops with a cold joint where the slab was supposed to be continuous; order long and you've paid for material you now have to dispose of. The calculation itself is straightforward volume geometry plus a sensible waste allowance, but the unit conversions (cubic metres, cubic yards, bags) are where orders go wrong.
The concrete tools here take dimensions in whatever units you measured, handle the conversions, apply a stated waste factor you can see and change, and translate the result into both ready-mix volume and bag counts.
Using the results
Volume is the calculator's job; everything else about a good pour — subgrade preparation, reinforcement, mix specification, curing — is the part that determines whether the slab lasts. For structural work, the mix design and thickness should come from the engineering or the code applying to your project, not from a volume calculator. Use the number here to order; use your local requirements to build.