Concrete Calculator
Measure one pour or combine several. Calculate the concrete itself first, then add your chosen ordering allowance and, if you are using bagged concrete, your exact manufacturer yield.
Build your concrete quantity
Add each separate pour, choose metric or imperial measurements, then keep the measured volume and ordering allowance visible as separate numbers.
Use the shape that matches what is actually being poured
The basic rule is always geometric volume, but the dimensions you need change with the job. A slab or pad uses length × width × depth. A circular slab uses π × radius² × depth. A cylindrical post hole or pier uses the same circle formula with the hole diameter and its vertical depth. Strip footings are rectangular volumes, but keeping them labelled separately makes a multi-pour job easier to check.
Measured quantity first, buying quantity second
The calculator deliberately reports the measured volume before any allowance. That gives you a number you can verify from drawings or site measurements. Your selected allowance is then shown as its own volume before the final order quantity is displayed. This prevents a common problem: an unexplained “waste factor” being hidden inside the answer.
Bagged concrete: enter yield, not a guessed universal bag rate
A bag’s weight does not, by itself, tell you the exact volume of finished concrete it produces. Products differ. Enter the finished-concrete yield printed in the manufacturer’s technical information or packaging. The calculator shows both the fractional mathematical requirement and the whole number of bags to purchase.
Important: this is quantity planning, not mix design or structural design. Concrete grade, reinforcement, slab thickness, foundations and suitability depend on the actual project. Follow the project specification and product information.
Why multiple pours matter
Real jobs are often not one rectangle. A base may have a main slab plus a threshold, pads or separate footings. Adding each pour separately lets you check the dimensions and subtotal logic rather than forcing everything into one approximate rectangle.
Next step: are you planning the whole slab build-up?
If you also need excavation and sub-base quantities, use the complete concrete slab materials estimator. If the volume is already known and you are preparing to buy, the concrete ordering guide explains measurement checks, bagged versus delivered concrete and supplier constraints. Our calculation methodology explains allowances and purchasing-rounding principles.