Concrete Curb and Gutter Calculator

How to use this calculator

The question behind most of these jobs is just how much concrete for curb and gutter a given run takes, and the answer is one number off the section drawing. Enter the five dimensions below and the calculator returns the curb and gutter volume three ways: the cross sectional area in square feet, the total cubic yards of concrete for curb and gutter over your run, and the yards per 100 linear feet, which is the rate you reuse on the rest of the job.

1. Pull the dimensions off your local standard drawing first. Public work is built to a state DOT or city section such as CG-6 or a Type A, and the inspector signs off against that drawing, not against an estimate.
2. Enter the curb height above the pan, which is the exposed face height, and the curb width across the top of the block.
3. Enter the gutter pan width from the face of the curb out to the pavement edge. Twenty four inches is the workhorse width; 18 inches is common on residential streets.
4. Enter the section thickness, meaning how deep the pan sits. Six to eight inches is typical, usually matching the pavement next to it.
5. Add a fillet only if your section drawing shows a triangular haunch where the curb face meets the pan. Leave both fillet boxes blank when the section is a plain curb sitting on a flat pan.
6. Enter the run length, keep a 10 percent waste allowance, and read the cubic yards per 100 feet from the result panel.

The formula

Break the section into simple shapes, add up the areas, then run that cross-section down the length of the job:

Cross-section ft² = (Curb height ft × Curb width ft) + (Pan width ft × Thickness ft) + (0.5 × Fillet base ft × Fillet height ft)
Cubic yards = Cross-section ft² × Length ft ÷ 27

The fillet term is half the base times the height because a haunch is a triangle. Leave it out and the two rectangles are all you need.

Worked example. A standard section with a 24 inch pan 6 inches thick and a 6 inch by 6 inch curb standing on top of it. In square inches the pan is 24 × 6 = 144 and the curb is 6 × 6 = 36, so the section is 180 square inches. Divide by 144 and the cross-section is 1.25 square feet. Over a 100 foot run that is 125 cubic feet, or 125 ÷ 27 = 4.63 cubic yards. Add 10 percent and you would order 5 yards.

Estimators think in yards per 100 linear feet because that number travels well: once you know a section takes 4.63 yards per 100 feet, an 850 foot job is roughly 39 yards without touching the geometry again. The calculator prints that rate for you, which is how a curb and gutter estimate normally gets built, as a curb and gutter per linear foot rate carried across the quantity on the plan sheet rather than a fresh volume every time. Keep the yardage and the rate together when you hand it to anyone else: the rate is what a reviewer checks, and the gutter pan volume inside it is what people get wrong.

Pouring a plain curb with no gutter pan? Use the concrete curb calculator, which drops the pan out of the section entirely. For the steps on site, see how to pour a concrete curb.

Standard sections and what they take

Combined curb and gutter is almost always built to a named section, and the name usually encodes the dimensions. NCDOT buys it as a 1 foot 6 inch and a 2 foot 6 inch curb and gutter, both named pay items. Iowa SUDAS specifies a 6 inch high, 6 inch wide curb with a 2 foot 6 inch gutter. Minneapolis uses a 6 inch curb top in an 8 inch section on ordinary streets and a 12 inch top in a 14 inch section downtown and on its parkways, often with a 1 foot gutter pan. Montana DOT's detail asks for a 3 foot minimum gutter width at 7 inches thick. NYC's integral curb and gutter runs a 6 inch top with a gutter of 6 to 12 inches. Here is what each of those takes, straight from the same engine as the calculator above with no waste added.

The spread at the bottom of that table is the thing to notice. The narrowest and widest published sections differ by a factor of four for the same 100 feet of street. If you are bidding against someone else's drawing, the pan width is where the money is. The curb height guide sets out what a dozen agencies publish for face height, the curb dimensions reference covers top width and pan width, and the curb and gutter guide covers the profiles themselves.

The pan is most of the concrete

People size a curb and gutter order off the curb, and the curb is the small part. On the workhorse section above, the curb block is 0.25 square feet and the pan is 1.00 square foot, so 80 percent of the concrete is the flat part you walk on. On Montana's 36 inch pan it is 87 percent. Widening the pan from 18 inches to 30 inches adds half a square foot of section, which is twice the entire curb block, and it adds 1.86 cubic yards for every 100 feet of run.

Two things follow from that. First, get the pan width right before you worry about the curb: an inch of error on the pan costs you more concrete than an inch of error on the curb face. Second, a combined section is a flatwork order in disguise, which is why slipform crews and bid prices treat it differently from plain curb. Our curb cost guide has the installed price spread, and the curbing machine guide covers where extrusion stops being practical.

Cross slope, and whether the pan bottom is level

A gutter pan is built to a cross slope so water runs to the flow line, and published slopes vary enormously: Seattle wants 1 to 4 percent with 2 percent preferred, Wisconsin DOT fixes 4 percent unless the plans say otherwise, Montana uses 4 percent, Caltrans sets 8.33 percent and says flatter "should be avoided," and Tennessee DOT publishes 0.085 feet per foot, which is 8.5 percent. That is an eight-fold spread for the same strip of concrete.

For your concrete order, the cross slope itself does not change anything, as long as the bottom of the pan follows the top. Tilting a rectangle does not change its area, so a sloped pan of constant thickness takes exactly the concrete the calculator says. What does change the order is pouring the pan on a level bottom, which is a real option: Wisconsin DOT's standard detail says in a general note that "the bottom of curb and gutter may be constructed either level or parallel to the slope." Build it level and you have added a wedge of concrete across the pan.

The wedge is a triangle, so you can price it. On a 24 inch pan, a 4 percent cross slope rises about 0.96 inches across the pan, which is 11.5 extra square inches, 6 percent more concrete. At Caltrans' 8.33 percent the rise is 2 inches, which is 24 square inches and 13 percent more. If your section is poured on a level bottom, add the triangle as a fillet: put the pan width in the fillet base box and the rise in the fillet height box, and the calculator folds it in. The concrete slope calculator converts between percent, ratio and inches of fall per foot if your drawing uses a different unit from your tape.

When to use the fillet boxes

The fillet is the triangular haunch some sections carry where the back of the curb meets the pan, or where the pan thickens into the curb block. Leave both boxes blank unless your section drawing actually shows one, because it is not a small term: a 6 inch by 6 inch haunch adds 0.125 square feet to a 1.25 square foot section, which is 10 percent, or 0.46 cubic yards per 100 feet.

Three legitimate uses for those boxes. One, a genuine haunch on the drawing, entered at its drawn base and height. Two, the level-bottom wedge described above. Three, a thickened edge where the pan meets the pavement, which some agencies detail and some do not. If you are unsure whether the shape on your sheet is a haunch or a bevel, measure it: a haunch adds concrete and a bevel takes it away.

The gutter depression at an inlet, which no per-foot rate includes

Everything above prices a constant section. Where the pan reaches a storm inlet it stops being constant, because the gutter is warped down into a local depression so the flow concentrates at the throat. Iowa SUDAS details the standard open-throat depression at 6 inches deep and 3 feet wide, with 1.5 feet the minimum width, and says of it that "this depression aids in increasing the interception capacity of the intake." It is a drainage feature, but it is also concrete, and a yards-per-100-feet rate will never contain it.

Price it off your own detail, because the transition either side of the throat is what sets the volume and it comes off the standard drawing rather than a rule of thumb. Take the length of gutter the warp affects, multiply by the pan width, then multiply by the average extra depth, which is about half the depression depth where the warp runs out in a straight line. A 6 inch depression on a 3 foot pan warped out over 10 feet of gutter averages roughly 3 inches of extra depth, so 10 × 3 × 0.25 = 7.5 cubic feet, or 0.28 cubic yards at that one inlet. Three inlets on a job is most of a yard nobody added.

Two other places the constant section breaks down. A driveway crossing is a driveway apron with its own thickness, normally deeper than the pan. A curb return at an intersection carries the section around a radius, so measure the run along the flow line rather than the back of curb or you will come up short. The curb and gutter guide works through how inlets, returns and valley gutters interrupt a run, and why the depression changes the effective cross slope the drainage design is solving against.

Base course, and what to order besides concrete

Most of the disagreement between agency details is not about the concrete at all, it is about what goes under it. FHWA's Federal Lands standard drawing requires you to "place 3 inches minimum aggregate bed course under all curb and gutter." MoDOT asks for 4 inches of Type 5 aggregate. Sacramento County and Santa Barbara both want 6 inches of base compacted to 95 percent. Ohio DOT requires none at all, saying to set the curb on a thoroughly compacted subgrade, with a 3 inch porous bed only on clay. Wisconsin DOT puts base in only "at the locations, thickness and section the plans show."

So the trench you dig is deeper than the concrete by whatever your drawing says, and the base is a separate order. A 3 inch base under a 2 foot wide trench is 50 cubic feet, 1.85 cubic yards, or about 3 tons of aggregate per 100 feet at the 1.6 tons per compacted yard the calculators use; the gravel calculator will do it from your own trench dimensions. If the section is tied to the pavement with bars, which Wisconsin DOT requires on five of its curb and gutter types, the rebar calculator handles the steel.

Joints are the other thing the drawing decides. Contraction joint spacing across the specs we have read runs from 5 feet to 25 feet, with 10 feet by far the most common, and expansion joints run from 30 feet to 400 feet, which is a 13-fold spread. The curb and gutter guide works through why the location matters more than the interval, and how to pour a concrete curb covers cutting them on site.

Ordering, and the truck minimum

The workhorse section at 100 feet is 4.63 cubic yards, or 5.09 with the recommended 10 percent waste. That is still under the 10 cubic yard truck minimum, so a short 100 foot section pays the $30 per yard short load fee on top of the $160 per yard delivered price. You clear the minimum at about 215 feet of that section, which is worth knowing if you have two short runs you could pour the same morning.

Bagging a combined section is not realistic. Five cubic yards is 230 eighty-pound bags, and the pan has to be struck off and floated while the curb is still plastic, so it is a continuous pour by nature. Give the plant the total yards and the yards per 100 feet, which is the figure that tells a dispatcher whether the truck can chute it or you need a pump. Labor is bid by the foot: the cost estimate above is pre-filled at $5 to $15 per linear foot, with $9 as the middle for hand-formed work, and the low end assumes a long slipformed run.

Pouring a plain curb with no pan is the concrete curb calculator. A driveway crossing the section is a driveway apron, which the city specifies and inspects. The flatwork behind the curb is the sidewalk calculator or the slab calculator, and if you only need the volume from an area and a depth, the cubic yard calculator does that in one step.