Concrete Slab Calculator
Planning a patio, shed pad, walkway or driveway slab? This calculator tells you exactly how much concrete you need — in cubic yards for a ready-mix truck, or in 80 lb / 60 lb bags for a DIY mix — plus an estimated 2026 cost range based on national US prices.
Enter your slab dimensions below. Results update instantly as you type, including the 10% extra you should always order for spill and uneven subgrade.
Patios & walkways: 4 in · Driveways: 5–6 in
- Slab volume (exact)
- 1.23 cu yd
- Order with 10% extra
- 1.36 cu yd
- 80 lb bags (exact volume)
- 56 bags
- 60 lb bags (exact volume)
- 75 bags
- Ready-mix truck cost (est.)
- $170 – $244
- Bagged concrete cost (80 lb)
- $280 – $392
Bag counts are for the exact volume — buy 1–2 extra bags as buffer. Cost ranges are national US averages; delivery/short-load fees not included.
How This Calculator Works
Volume (yd³) = Length(ft) × Width(ft) × [Thickness(in) ÷ 12] ÷ 27 → × 1.10 safety factor- Convert thickness from inches to feet by dividing by 12 (4 in = 0.333 ft).
- Multiply length × width × thickness in feet to get cubic feet.
- Divide by 27 (one cubic yard = 27 cubic feet) to get cubic yards.
- Multiply by 1.10 — concrete pros order about 10% extra for spill, uneven subgrade, and settling.
- For bagged concrete: an 80 lb bag yields ≈ 0.60 cu ft, a 60 lb bag ≈ 0.45 cu ft. Divide your cubic feet by the bag yield and round up.
Example: A 10 ft × 10 ft slab at 4 in thick: 10 × 10 × 0.333 = 33.3 cu ft ÷ 27 = 1.23 yd³ exact → order 1.36 yd³ (about 56 × 80 lb bags, or 1.5 yards from a truck).
Frequently Asked Questions
How many 80 lb bags of concrete are in a cubic yard?
One cubic yard equals 27 cubic feet, and an 80 lb bag yields about 0.60 cubic feet — so it takes roughly 45 bags of 80 lb concrete mix to make one cubic yard.
How much concrete do I need for a 10×10 slab?
A 10 ft × 10 ft slab at 4 inches thick needs about 1.23 cubic yards — order 1.4 yards (or ~56 80-lb bags) after adding the standard 10% safety factor. At 6 inches thick the same slab needs about 1.85 yards exact.
Should I order a ready-mix truck or use bags?
Rule of thumb: under about 1 cubic yard, bags are manageable for DIY (a yard is ~45 × 80 lb bags — a lot of mixing). Above 1–1.5 yards, a ready-mix delivery is usually cheaper per yard and far less labor. Many suppliers impose short-load fees under 3 yards, which is reflected in the per-yard price range.
How thick should a concrete slab be?
4 inches is standard for patios, walkways and shed pads. Driveways that carry vehicles typically need 5–6 inches with rebar or wire mesh, and footings under structures usually require 8–12 inches — check your local code.
How much does concrete cost in 2026?
Nationally, ready-mix concrete runs roughly $125–$180 per cubic yard delivered, and an 80 lb bag of Quikrete-style mix costs about $5–$7 at home improvement stores. Prices vary significantly by region and by delivery distance.
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Last updated: 2026-10-25