What it works out
Choose slab or footing. A slab takes length, width and thickness; a footing takes length, width and depth. You get the volume, an order quantity and an estimated weight. Waste is added first, then the order rounds up to the purchase step in Settings, a quarter cubic yard to start with. Weight uses your stored concrete density. No deduction is made for rebar and nothing is added for over-digging or formwork loss.
You enter
- Length
- Width
- Depth
The formula
- Slab volume
- length × width × thickness
- Footing volume
- width × depth × length
- Weight
- order × density
In words: Slab volume = length times width times thickness; footing volume = width times depth times length; weight = order times density
Worked example
A 10 ft by 10 ft slab, 4 in thick
- Length 10 ft
- Width 10 ft
- Thickness 4 in
- Thickness = 4 ÷ 12 = 0.3333 ft
- Volume = 10 × 10 × 0.3333 = 33.33 ft³
- In cubic yards: 33.33 ÷ 27 = 1.23 yd³
Waste is then added and the order rounds up to the purchase step in your settings, a quarter cubic yard to start with.
Good to know
- No deduction for rebar; nothing added for over-digging or formwork loss.
- Weight uses the concrete density you store in settings.
- A calculator, not a building-code check: confirm local rules with your building authority.
Questions
How much extra should I order?
Waste is your choice; the tool adds it before rounding up. Many crews add a little for uneven ground.
Does it do footings?
Yes. Choose footing and enter width, depth and length.