Concrete Calculator
Slabs, footings & pours
Use this free concrete calculator to figure out exactly how much concrete you need for a slab, footing, sidewalk, patio, driveway or post hole. Enter your dimensions and instantly get cubic yards, cubic meters, the number of 60 lb bags and an estimated total cost — no signup, no math required.
Formula
Imperial: (L ft × W ft × D in / 12) / 27 = yd³
Metric: L m × W m × D cm / 100 = m³
Final = volume × (1 + waste / 100)
About this calculator
Use this free concrete calculator to estimate ready-mix or bagged concrete for slabs, footings, sidewalks, patios and driveways. Get instant cubic yardage, cubic meters, 60-lb bag count and total project cost.
Frequently asked questions
▸How is concrete volume calculated?
Volume = length × width × depth. Convert depth to match length units, then convert to cubic yards or meters.
▸Why add a waste factor?
Spillage, uneven subgrade, and over-excavation typically require 5–10% extra concrete.
▸How many bags of concrete do I need?
A standard 60 lb bag yields about 0.017 cubic yards.
Example calculations
A standard 10×10 patio slab at 4 inches deep needs about 1.23 cubic yards of concrete (≈ 73 bags of 60 lb). Add 10% waste for a safer order of 1.36 yd³.
A single fence post hole holds about 0.087 cubic yards (≈ 5 bags of 60 lb). For 10 posts, plan on roughly 0.9 yd³ of concrete.
A small driveway pour comes to about 4.44 yd³ before waste. Ready-mix is usually the most cost-effective option above 3 yd³.
Concrete Calculator FAQ
▸How much concrete do I need for a 10x10 slab?
A 10×10 slab at 4 inches deep needs about 1.23 cubic yards or 73 bags of 60 lb concrete. Add a 10% waste factor for over-excavation.
▸How many bags of concrete in a cubic yard?
There are roughly 60 bags of 60 lb concrete or 45 bags of 80 lb concrete in one cubic yard.
▸How is concrete for a post hole calculated?
Volume = π × r² × depth. A 12-inch wide, 36-inch deep hole holds about 0.087 cubic yards of concrete.
▸Should I order ready-mix or bagged concrete?
Ready-mix is typically cheaper and faster above 2–3 cubic yards. Below that, bagged concrete is more practical.
▸Why add a waste factor?
Spillage, uneven subgrade and over-digging usually require 5–10% extra concrete to avoid running short mid-pour.