Concrete Volume Calculator – How Much Concrete Do You Need?
Estimate concrete quantities for any project with our concrete volume calculator. Compute cubic yards or meters for slabs, columns, footings, and walls to avoid over-ordering.
Recommended: 5-10% for slabs, 10-15% for complex shapes
Concrete volume is just length × width × depth for rectangular shapes. For a 10×12 foot slab that's 4 inches thick: 10 × 12 × 0.33 = 40 cubic feet, or about 1.5 cubic yards. Add 10% for waste and you order 1.65 yards.
Volume Formulas
Slab/Footing: Length × Width × Depth
Wall: Length × Height × Thickness
Column: π × (diameter/2)² × Height
The waste factor matters more than people think. Spillage, over-excavation, and form bowing all eat concrete. A 10% waste factor means ordering 1.1 cubic yards for every 1 yard calculated. For complex forms or pump trucks, bump it to 15%.
| Project Type | Waste Factor | Why |
|---|---|---|
| Simple slab on grade | 5-7% | Minimal formwork, easy pour |
| Standard footings | 7-10% | Some trench over-excavation |
| Columns and walls | 10-12% | Form work complexity, spillage |
| Complex shapes/stamped | 12-15% | Cutting waste, pattern matching |
| Pump truck delivery | +3-5% | Concrete left in pump lines |
| Bag Size | Yield (cubic feet) | Yield (cubic yards) | Bags per Cubic Yard |
|---|---|---|---|
| 40 lb bag | 0.30 cu ft | 0.011 cu yd | 90 bags |
| 60 lb bag | 0.45 cu ft | 0.017 cu yd | 60 bags |
| 80 lb bag | 0.60 cu ft | 0.022 cu yd | 45 bags |
Yields are approximate and vary by brand and water content. Quikrete and Sakrete have slightly different formulations.
| Project | Dimensions | Volume (no waste) | With 10% Waste |
|---|---|---|---|
| 10×12 patio, 4" thick | 10′ × 12′ × 0.33′ | 1.48 cu yd | 1.63 cu yd |
| 24×24 garage slab, 5" thick | 24′ × 24′ × 0.42′ | 8.89 cu yd | 9.78 cu yd |
| Deck footing, 4 columns | 12" dia × 36" deep | 2.62 cu yd | 2.88 cu yd |
| Retaining wall | 20′ × 4′ × 1′ | 2.96 cu yd | 3.26 cu yd |
How do I convert cubic feet to cubic yards?
Divide cubic feet by 27. There are 27 cubic feet in a cubic yard (3×3×3). A 10×10 slab at 4 inches is 33 cubic feet, which equals 1.22 cubic yards. Ready-mix companies sell by the yard, not by the foot.
Should I buy bags or ready-mix?
Bags make sense for projects under 1 cubic yard – a small patio, post holes, or repairs. Anything over 2 yards and ready-mix delivery is cheaper and less labor. Between 1-2 yards, it depends on your access and back strength.
What happens if I order too little concrete?
Ready-mix companies charge "short load" fees for orders under their minimum (usually 4-5 yards). If you're short mid-pour, you're in trouble – concrete sets in 90 minutes. Always round up. Leftover concrete can be used for stepping stones or garden edging.
How thick should a concrete slab be?
Residential patios and sidewalks: 4 inches. Driveways: 5-6 inches (more if you park heavy trucks). Shop floors: 6 inches minimum. Garage floors with lifts: 6-8 inches with rebar. Thicker isn't always better – proper subgrade preparation matters more.
Do I need rebar in my concrete?
For slabs on grade (patios, sidewalks), welded wire mesh is usually enough. Driveways and structural slabs need rebar – typically #3 (3/8") or #4 (1/2") bars on 18-inch centers. Columns and footings always need vertical rebar. Check local codes.
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