CalcStack — free, instant, no signup. The interactive calculator loads automatically.

Concrete Calculator

Slabs, footings, posts — ordered right the first time.

Concrete has a brutal property: you cannot pause mid-pour to buy more. Ordering short means a cold joint and a weakened slab; ordering long is money hardening in the truck. This calculator converts your dimensions to cubic yards for ready-mix orders and to exact bag counts for the mixer-in-a-wheelbarrow approach, so the pour finishes in one go.

Why people use this

A concrete pour cannot pause while you buy more — ordering short ruins the slab. People use this to size ready-mix orders and bag counts for patios, walkways, and footings, and to decide the bags-versus-truck question (the crossover is about one yard).

How it works

1. Enter the slab length and width in feet.
2. Enter thickness: 4 inches is standard for patios and walkways, 5–6 for driveways, 6+ for heavy loads.
3. The calculator computes cubic yards (the ready-mix unit) and cubic feet.
4. Bag counts use standard yields: 80 lb ≈ 0.6 cu ft, 60 lb ≈ 0.45 cu ft.

Common questions

When is ready-mix worth it over bags?

The crossover is around 1 cubic yard: that is 45 bags of 80 lb mix — hours of brutal mixing — versus a single truck delivery. Most pros say bags under a yard, truck over it, and always order 5–10% extra.

How thick should a concrete driveway be?

4 inches handles passenger cars on good soil; 5–6 inches is the common standard for durability, and 6+ with reinforcement for trucks or poor subgrade. Thickness is cheaper than replacement.

How many 80 lb bags make a yard of concrete?

About 45 bags per cubic yard (27 cu ft ÷ 0.6 cu ft per bag). The 60 lb size takes about 60 bags. The calculator shows both counts for your exact slab.

Browse all 500+ free calculators →