Curb & Gutter Calculator

How to Calculate Concrete for Curbs and Gutters

Curb and gutter calculations differ from slab calculations because you're working with a linear profile rather than a flat area. The key is calculating the cross-sectional area of the curb profile, then multiplying by the total length.

The Curb Concrete Formula

Volume (CY) = Cross-Section Area (SF) × Length (ft) ÷ 27

For a standard 6" × 6" curb, the cross-section area is 0.5 ft × 0.5 ft = 0.25 SF. For 100 linear feet: 0.25 × 100 ÷ 27 = 0.93 CY.

Adding the Gutter

A standard curb-and-gutter profile adds a 12–24" wide gutter slab (typically 4" thick) behind the curb. This significantly increases your concrete volume. A 100 LF curb-and-gutter section with a 12" gutter adds about 0.37 CY — nearly 40% more concrete.

Curb Concrete Specifications

Municipal and DOT specs typically require:

• Minimum 4000 PSI — higher strength for freeze-thaw durability
• 4–6% air entrainment — required in freeze-thaw climates for scaling resistance
• Low water/cement ratio — 0.45 or less for durability
• Fiber reinforcement — polypropylene fibers reduce cracking, often specified in lieu of rebar for small curbs

Curb Machine vs. Hand Forming

For jobs over 200 linear feet, a slip-form curb machine (curb and gutter machine) is almost always more cost-effective than hand-forming. The machine is faster, more consistent, and produces a better surface. For shorter runs or complex radius work, hand-forming with wood or steel forms is the standard approach.

Expansion Joints and Control Joints

Curbs require control joints every 10–15 feet (saw cut or tooled) and expansion joints every 50–100 feet. Budget for expansion joint filler material at $2–3 per linear foot at expansion joint locations.

Cost per Linear Foot — What to Expect

Need a Professional Estimate?

Use our Pro Estimate Template to turn these calculations into a professional bid sheet for curb and flatwork projects.