Free estimator
Concrete Calculator
Use this concrete calculator to estimate volume, cubic yards, bag quantities, waste allowance, and optional cost for slabs, pads, walkways, and small pours.
Last updated: June 23, 2026
How to measure
Measure the slab length, width, and planned thickness. Use the actual formed dimensions where possible. For irregular areas, divide the pour into smaller rectangles and add the results together.
Formula
cubic feet = length(ft) x width(ft) x thickness(in) / 12
cubic yards = cubic feet / 27
80 lb bags = cubic feet / 0.6
Tips before buying
- Check local requirements for base preparation, reinforcement, and slab thickness.
- Confirm bag yield on the product label before purchasing.
- Plan mixing, placement, screeding, and finishing before concrete starts setting.
FAQ
How much extra concrete should I order?
A 10% waste allowance is a common planning estimate for uneven subgrade, form variation, spills, and small measurement errors.
How many cubic feet does an 80 lb bag of concrete make?
An 80 lb bag is commonly estimated at about 0.6 cubic feet. Always check the bag label for the exact product yield.
When should I order ready-mix instead of bags?
Bagged concrete can work for small projects. Larger slabs may be easier and more consistent with ready-mix delivery.