How much concrete do I need?
Enter the length, width and thickness of your slab, footing or pad. You'll get the volume in cubic yards and cubic metres, plus how many bags of pre-mix it takes — instantly.
Order about 0.99 m³ to allow ~10% for spillage and an uneven base.
Typical pre-mix yields — add a couple of spare bags. Buy ready-mix by the m³ for larger pours.
Volume = length × width × thickness. Thickness is entered in millimetres (slabs are thin).
Common questions
- How much concrete do I need?
- Multiply length × width × thickness in the same units, then convert to cubic yards or cubic metres. A 10 ft × 10 ft slab at 4 inches thick is about 1.23 cubic yards (0.94 m³). Order roughly 10% extra for spillage and an uneven base.
- How do I calculate concrete volume?
- Volume = length × width × thickness. Keep thickness in the same unit (4 inches = 0.33 ft; 100 mm = 0.1 m). The calculator does this for you and converts to cubic yards, cubic feet and cubic metres.
- How many bags of concrete are in a cubic yard?
- A cubic yard is 27 cubic feet. At about 0.6 ft³ per 80 lb bag that's roughly 45 bags of 80 lb mix per cubic yard, 60 bags of 60 lb, or 90 bags of 40 lb. Past about a cubic yard, ordering ready-mix is usually cheaper than bags.
- How thick should a concrete slab be?
- As a general guide, 4 inches (100 mm) suits patios, walkways and shed bases, and 5–6 inches (125–150 mm) suits driveways or anything carrying vehicles. Structural slabs and footings are governed by your local code and engineering — check the requirement for your area.
- Is this a concrete slab calculator?
- Yes. For a slab, enter its length, width and thickness and the tool returns the volume in cubic yards (the “yardage”), cubic feet and cubic metres, plus how many bags of concrete or cement mix it takes — so it works as a slab, yardage and bag calculator in one.
Want the full walk-through? Read the concrete guide →
Reference & education only. Not professional, engineering, or code-compliance advice. Estimates are based on published model codes; local amendments and your Authority Having Jurisdiction (AHJ) govern. Always verify against the current adopted code and a licensed professional before doing work.
Last reviewed 2026-06.