Concrete Sidewalk Calculator
Short answer: a 30 ft long, 4 ft wide sidewalk at 4 inches thick needs 1.48 cubic yards — about 74 × 80 lb bags with 10% waste — with 3 control joints making 4 panels.
Calculate your sidewalk
How the calculation works
Volume = length × width × thickness ÷ 12 (cubic feet), then ÷ 27 for cubic yards. Joints are counted along the length: interior joints = length ÷ joint spacing, rounded down, and panels = joints + 1.
Worked example: 30 × 4 ft at 4 in = 40 cu ft = 1.48 cubic yards net. With 10% waste: 1.63 cubic yards, about 74 × 80 lb bags. At 8 ft joint spacing: 3 interior joints, 4 panels.
Common walkways (4 inches thick, net)
| Walkway | Volume | 80 lb bags |
|---|---|---|
| 3 × 20 ft | 0.74 cubic yards | 34 |
| 3 × 30 ft | 1.11 cubic yards | 50 |
| 4 × 30 ft | 1.48 cubic yards | 67 |
| 4 × 50 ft | 2.47 cubic yards | 112 |
Volumes are net (before waste). Bag counts use the 0.60 cu ft yield per 80 lb bag, rounded up.
Frequently asked questions
How much concrete for a 3x30 sidewalk?
At 4 inches thick: 1.11 cubic yards net (1.22 with 10% waste), about 50 × 80 lb bags net (55 with waste).
How thick should a sidewalk be?
4 inches is typical for a walkway carrying foot traffic only. Use 5–6 inches where vehicles will cross it, such as a driveway apron.
How far apart should sidewalk joints be?
24 to 36 times the slab thickness, capped at 15 ft — about 8 to 10 ft for a 4-inch sidewalk. Cut joints at least one-quarter of the thickness deep, and at least 1 inch deep.