Curb and Gutter Calculator

This is an estimate, not professional advice. Check your inputs and verify the result against your plans and local building code before you build or order. See terms and disclaimer.

How this calculator works

Enter your dimensions and the result updates instantly. A waste allowance is included so you order slightly over rather than running short mid-pour, and ready-mix is rounded up to the nearest quarter yard, which is how it is sold.

Worked example

A 50 ft run with a 6 inch curb (6 inches deep) and a 24 inch gutter flag 6 inches thick, with a 10% waste allowance. Inputs: Curb height 6 in, Curb depth (width) 6 in, Gutter width 24 in, Flag (gutter) thickness 6 in, Run length 50 ft, Number of runs 1, Waste allowance 10 %. Result: 2.55 yd³ (about 115 × 80 lb bags).

Concrete for common curb and gutter runs

Calculated with a 6 inch curb, 6 inch depth, 24 inch gutter flag 6 inches thick, and 10% waste. Tap a length to load it above.

Method & assumptions

A curb and gutter barrier is a continuous concrete shape with two parts: the raised curb and the flat gutter pan, or flag, beside it. Seen end-on, the concrete fills an L-shaped section. We work out the area of that section, then multiply by the length of the run to get the volume, the same way every other linear pour is estimated.

The section area is the curb (its height times its depth) plus the gutter flag (its width times its thickness), all in inches, which gives square inches. We divide by 144 to convert to square feet, multiply by the run length in feet and the number of identical runs, add your waste allowance, and divide by 27 for cubic yards. Ready-mix is rounded up to the nearest quarter yard, which is how it is sold, and bags are rounded up.

This estimates a solid poured section. A machine-extruded or slip-formed curb uses the same volume, and the estimated weight, at about 150 pounds per cubic foot of normal concrete, helps you plan forms and subgrade. Curb and gutter usually carries light reinforcement and needs a compacted base and proper joints, so confirm the profile, the base and the spacing of contraction joints against your plans and local public-works standard.

Pro tips and common mistakes

• Compact the subgrade first. Curb and gutter cracks and settles over a soft or uneven base. Pour onto a firm, compacted subgrade or a thin aggregate base, not loose soil.
• Match the standard profile. Most towns publish a curb and gutter detail with set heights and widths. Use those dimensions so the pour passes inspection and drains correctly.
• Keep the gutter draining. The flag has to fall toward the inlet, not pond. Hold a slight slope along the run and check it with a string line before you pour.
• Cut contraction joints. Tool or saw joints at regular spacing, often every 10 to 15 feet, so the curb cracks at the joints rather than at random. It controls cracking and looks clean.
• Order a little extra. A long run eats concrete fast and you cannot top up once it sets. The waste allowance and rounding up cover an uneven base and spillage.

Frequently asked questions

References

• Curb (road) (Wikipedia)
• ACI 332: Residential concrete code
• QUIKRETE Concrete Mix yield (spec sheet)

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