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Calculators & guides

Concrete Curb Calculator

Estimate a rectangular curb and its adjoining flag or gutter as two non-overlapping solid prisms.

Units

Geometry dimensions — schematic, not to scaleCG (clear)HTL = pour length
Schematic · not to scale · quantity repeats the entire solid

Beside the curb, not including curb width.

Concrete & bag assumptions

Density is the placed concrete density, not dry bag weight. Defaults are examples for normal-weight concrete. Bag weight does not determine yield; use the mixed yield printed on your product.

Estimate cost (optional · USD)

All cost fields are optional and user-entered. Ready-mix and bags are alternatives, never added together. No average or local prices are assumed — use a real quote. Labor per area is available only for shapes with a defined footprint.

Formula & solid model

V = L × [C × (H + T) + G × T] × Q

All lengths convert to metres before calculation. Blank waste = 0%. Zero dimensions or quantity produce zero volume. Display values are rounded; costs and bags use unrounded volumes.

Rectangular curb prism: L × C × (H + T). Adjacent flag/gutter prism: L × G × T. G excludes the curb width, so the base under the curb is counted exactly once. No battered faces or gutter slopes are assumed.

Curb & gutter · incl. 10% waste

You need approximately 1.019 cubic yards

27.5 ft³ · 0.779 m³ · 778.71 litres

Volume

UnitExact+10% waste
Cubic yards0.9261.019
Cubic feet2527.5
Cubic metres0.7080.779
Litres707.921778.713

Placed weight · incl. waste

4,125 lb / 1,871.07 kg

Density: 150 lb/ft³ · weight = volume × density

Selected premix bags · incl. waste

46 × 80 lb bags

Yield: 0.6 ft³ / bag · total volume ÷ yield, rounded up.

Above about 1 yd³, ready-mix is often more practical than mixing bags.

Estimate inputs & formula

Length (L): 20 ft · Curb width (C): 6 in · Curb above gutter (H): 6 in · Clear gutter width (G): 18 in · Flag / gutter thickness (T): 6 in · Quantity (Q): 1

V = L × [C × (H + T) + G × T] × Q

Clear gutter is beside the curb. Base under curb counted once; rectangular, unsloped cross-section.

Estimate only, not engineering advice. Actual needs vary with subgrade, forms and spillage. Confirm final quantities and product yields with your supplier or contractor before ordering.

What this calculates

C is the curb width. H is curb height above the gutter. T is the base/gutter thickness. G is the clear gutter width beside the curb, not the total width. The curb includes its own base, so no area is shared or counted twice.

This model has vertical curb faces and a flat gutter. Battered curbs, sloped gutters, fillets and other profiles need a separate cross-section calculation.

Formula

Curb = L × C × (H + T)

Adjacent gutter = L × G × T

Total = [curb + adjacent gutter] × quantity

Worked example

10 m long; C 0.2 m, H 0.15 m, G 0.5 m, T 0.1 m

  1. 1.Curb: 10 × 0.2 × (0.15 + 0.1) = 0.5 m³
  2. 2.Adjacent gutter: 10 × 0.5 × 0.1 = 0.5 m³
  3. 3.Total: 1 m³; with 10% waste: 1.1 m³

Common mistakes

  • Entering total curb-plus-gutter width as clear gutter width.
  • Adding the base below the curb again after including it in the curb prism.

Frequently asked questions

Does this account for a sloped gutter?

No. It explicitly models a rectangular curb and a flat rectangular gutter. Use your actual profile cross-sectional area for sloped or battered sections.