Cubic yards = length (ft) × width (ft) × thickness (ft) ÷ 27
Always convert inches to feet first by dividing by 12.
Slabs on grade
Example: a slab 60 ft × 40 ft, 4 inches thick.
- Thickness: 4 ÷ 12 = 0.333 ft
- Volume: 60 × 40 × 0.333 = 800 cubic feet
- Cubic yards: 800 ÷ 27 = 29.6 CY
Don't forget thickened edges and interior footings under the slab. Calculate them as separate beams and add them.
Continuous (strip) footings
Example: 200 linear feet of footing, 24 inches wide, 12 inches deep.
- 200 × 2.0 × 1.0 = 400 cubic feet
- 400 ÷ 27 = 14.8 CY
Measure footing length along the centerline so corners are not counted twice.
Spread (pad) footings
Example: 12 footings, each 5 ft × 5 ft × 18 inches.
- One footing: 5 × 5 × 1.5 = 37.5 cubic feet
- Twelve footings: 37.5 × 12 = 450 cubic feet
- 450 ÷ 27 = 16.7 CY
Walls
Example: a foundation wall 120 ft long, 8 ft high, 8 inches thick.
- Thickness: 8 ÷ 12 = 0.667 ft
- 120 × 8 × 0.667 = 640 cubic feet
- 640 ÷ 27 = 23.7 CY
Deduct large openings such as doors if they are significant.
Round columns and piers
Volume = 3.1416 × radius² × height
Example: 10 drilled piers, 24-inch diameter, 15 ft deep.
- Radius: 1 ft
- One pier: 3.1416 × 1 × 15 = 47.1 cubic feet
- Ten piers: 471.2 cubic feet ÷ 27 = 17.5 CY
Add waste the right way
Add a waste factor for spillage, over-excavation and uneven subgrade, but keep it on its own line. Footings poured against earth usually need more than formed walls. Showing net volume and waste separately lets you adjust and defend your number.
Beyond volume: what a full concrete estimate needs
Cubic yards are only part of the cost. A complete concrete estimate also includes:
- Rebar by size and weight, plus mesh and dowels
- Formwork contact area
- Vapor barrier and aggregate base
- Pumping, finishing, curing and testing
- Labor by element
Try our free concrete calculator for a quick check, or let us do the full takeoff. See concrete estimating services or send us your plans.