Concrete Curb Calculator

How it's calculated

The calculator finds the volume in cubic feet: length (ft) × width (ft) × height (in ÷ 12) — the same rectangle formula as a footing or sidewalk, just applied to a curb's typically narrow width and long length instead. That's converted to cubic yards by dividing by 27. A waste percentage is added on top to cover form loss and joint cutting along the run, and the adjusted cubic yardage is multiplied by concrete's density to get the weight in tons. Bag counts divide the adjusted cubic feet by each bag's yield; ready-mix truckloads divide the adjusted cubic yards by the truck's capacity — for a long run, the truckload number is often the one that matters.

Worked example

A 100 ft run of landscape curbing, 6 inches wide and 6 inches tall: volume = 100 × 0.5 × 0.5 = 25 cubic feet. In cubic yards, that's 25 ÷ 27 = 0.93 yd³. Adding a 10% waste factor: 0.93 × 1.10 = 1.02 yd³. At 2.02 tons per cubic yard, that's 1.02 × 2.02 = 2.06 tons — or 1.99–2.07 tons across the 1.95–2.03 density range. In 60 lb bags, the adjusted 27.5 cu ft (25 × 1.10) needs 62 bags — a run this long is usually a ready-mix job rather than a bagged one.

How deep should it be?

Curbs are almost always poured in sections rather than as one continuous run, and control or expansion joints mark where those sections meet — a long, thin, continuous strip of concrete is exposed to temperature swings along its whole length in a way a compact slab isn't, so it wants more frequent joints to control where it cracks as it expands and contracts, rather than leaving that to chance over a hundred-foot run. Forming a curb is a different job than forming a slab, too: a slab just needs a perimeter form around a flat area, while a curb needs a form on both sides for the entire run, shaped to hold the curb's specific cross-sectional profile — a rounded or angled top edge, a mow strip's flush-to-grade design, a driveway edge's particular reveal — plus flexible, bendable forming wherever the run curves. This calculator covers a site-formed, poured curb: concrete placed into a form built on site, the same basic method as a footing or sidewalk, just with a form on both sides of a narrow run instead of one perimeter. That's a different method from extruded curbing, where a machine pushes a stiff, low-slump mix through a shaped die in a continuous ribbon with no forms at all — common for commercial landscape curbing installers, and usually quoted and ordered through the company running that equipment rather than as a bagged or ready-mix material order. The volume math here applies to either method's concrete, but the equipment, mix design, and installation process are genuinely different, and this calculator assumes the poured, formed version. Curb width and height aren't numbers this calculator supplies — check your local code for a driveway edge or public right-of-way curb, or a landscape design plan for a mow strip or garden curb, and use the dimensions from there.

Common mistakes

• –Treating a curb like a slab and skipping section joints. A long, continuous run is exposed to temperature swings along its whole length in a way a compact slab isn't, and needs more frequent joints to control cracking, not fewer.
• –Forming only one side, or building a flat, slab-style perimeter form instead of shaping the form to the curb's actual cross-sectional profile on both sides of the run.
• –Confusing a poured, formed curb with extruded curbing. Extruded curbing uses a stiff mix pushed through a machine with no forms at all — a different method, mix, and equipment than the site-formed curb this calculator assumes.
• –Guessing at width and height instead of checking your local code for a driveway edge or right-of-way curb, or a landscape design plan for a mow strip or garden curb.
• –Underestimating how much a long run adds up. A modest 4-6 inch cross-section stretched over 100+ feet can reach a full ready-mix load faster than the narrow dimensions suggest.

Where the density figure comes from

Unlike the landscape materials on this site, concrete is a manufactured product with a tightly controlled mix, so its density varies far less than gravel, sand, or mulch — and the same figure applies whether it's poured as a slab, a curb, or any other normal-weight element. CEMEX, a major ready-mix producer, puts a solid unbroken pour at about two tons (4,000 lbs) per cubic yard. ACI 318 and ASTM C138 define normal-weight concrete at 145–150 lb/ft³ — ACI 318 uses 150 lb/ft³ as its default structural value — which works out to 3,915–4,050 lbs (1.96–2.03 tons) per cubic yard. The 1.95–2.03 ton/yd³ range here reflects that normal-weight span, not moisture variation. Lightweight and heavyweight concrete mixes fall outside this range and aren't covered by this calculator. We use 2.02 tons/yd³ as the display figure, drawn from:

• CEMEX — Ready-Mix Concrete Calculator
• ACI 318 & ASTM C138 — normal-weight concrete density, 145–150 lb/ft³

Read more in our density methodology.

FAQ

How wide and tall should a concrete curb be?

It depends on what the curb is for. A driveway edge or public right-of-way curb is often sized by local code; a landscape mow strip or garden curb comes from your own design plan. This calculator only converts whatever width and height you enter into a volume — it doesn't set those dimensions for you.

Why are curbs poured in sections instead of one continuous run?

A long, thin, continuous strip of concrete is exposed to temperature swings along its whole length in a way a compact slab isn't. Section joints — control or expansion joints — give that expansion and contraction a planned place to happen, instead of letting the curb crack randomly wherever it wants to over a long run.

What's the difference between a poured curb and extruded curbing?

A poured curb is placed into a form built on site, the same basic method as a footing or sidewalk. Extruded curbing uses a machine that pushes a stiff, low-slump mix through a shaped die in a continuous ribbon with no forms at all — common for commercial landscape curbing companies, and a genuinely different method, mix, and equipment from what this calculator assumes.

Why is a curb's width different from a slab's on this calculator?

Width here means the curb's cross-sectional width — typically 4 to 8 inches — not a broad area dimension the way it would for a patio or driveway. Length is the long run, often a hundred feet or more, which is why curbs get talked about by linear foot on a job site even though the underlying math is the same length × width × height.

What kind of form do I need for a curb?

A form on both sides of the entire run, shaped to hold the curb's specific cross-sectional profile — a rounded top, an angled edge, a flush mow-strip design — rather than the simple perimeter form a flat slab needs. Any curve in the run needs flexible, bendable forming to match.

Should I use bags or ready-mix for a curb?

It depends on the run's total length, not just its narrow cross-section. A short landscape curb can stay within reach of a bagged pour, but a long driveway edge or extended mow strip adds up fast — past roughly half a cubic yard, ready-mix delivery is generally cheaper and far less labor than mixing dozens of bags by hand.

Why does concrete's weight vary so little compared to gravel or sand?

Concrete is a manufactured product with a tightly controlled mix ratio, so its density is far more consistent than a quarried or organic material's. The range on this site comes from ACI 318 and ASTM C138's normal-weight concrete specification (145–150 lb/ft³), the same figures used across every concrete calculator here, not from moisture swings the way gravel, sand, or mulch vary.