Cement Calculator
Knowing how many bags of cement to buy before you start mixing saves you a mid-project run to the hardware store. Enter your project dimensions, pick a mix ratio, and this calculator tells you exactly how much cement, sand, and gravel you need.
Understanding Cement Mix Ratios
A mix ratio like 1:2:3 means 1 part cement, 2 parts sand, and 3 parts gravel by volume. The ratio you choose affects the strength and cost of your concrete.
Common mix ratios:
- 1:2:3 (Standard) -- Good for slabs, driveways, and general construction. Roughly 3,000 PSI.
- 1:1.5:3 (Strong) -- Higher cement content for structural elements and load-bearing work. About 4,000 PSI.
- 1:2:4 (Foundation) -- Works well for footings and foundation walls.
- 1:3:6 (Lean) -- Economy mix for non-structural uses like filling and leveling.
Why Dry Volume is Higher Than Wet Volume
When you mix dry cement, sand, and gravel with water, the smaller particles fill in the gaps between larger ones. That means you need about 54% more dry material than the final wet concrete volume. This calculator accounts for that automatically.
Bag Sizes
A standard 94 lb bag of Portland cement equals about 1 cubic foot. If your local store carries 80 lb bags instead, adjust the bag size setting to get the right count.