Concrete for a 3 × 20 Sidewalk at 4″
A 3 × 20 ft sidewalk poured 4 inches thick needs about 0.81 cubic yards (≈ 0.62 m³) of concrete (including a 10% waste buffer) — roughly 37 bags of 80 lb mix, weighing about 1.65 tons. Residential walkways are usually 4 inches thick.
This is under ~1 cubic yard — bagged mix (37 × 80 lb) is the practical choice.
Adjust the numbers
Pre-filled for a 3 × 20 ft slab — change anything to match your project.
A flat, solid pad of concrete — a patio, shed floor, walkway, or driveway. Measure how long and how wide it is, and how thick to pour it (4 inches is typical).
Bag & ready-mix counts include your 10% waste buffer.
Estimate only. These figures help you plan how much to buy — they are not engineering or structural advice. Actual needs vary with site conditions, waste, and installation method, so order a little extra and confirm final quantities with your supplier or contractor before you buy or start the job.
Other sidewalk sizes
Frequently asked questions
How much concrete do I need for a 3x20 sidewalk?
A 3 × 20 ft sidewalk at 4 inches thick contains 20 cubic feet of concrete — about 0.74 cubic yards. With a 10% waste buffer, order 0.81 cubic yards.
How many bags of concrete for a 3x20 sidewalk at 4 inches?
Roughly 37 bags of 80 lb mix, 49 bags of 60 lb, or 74 bags of 40 lb (including 10% waste). At this size, bagged mix is typically the practical choice.
How much does the concrete for a 3x20 sidewalk weigh?
About 1.65 tons (3,300 lb) of wet concrete.
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