How Tall Is a Curb?

How tall is a curb? Published heights by agency

A standard street curb stands about 6 inches tall. Six inches is the standard or typical face height in six of the twelve documents below, and it is the line at which TxDOT stops calling a curb mountable and starts calling it vertical. A blank cell means the document does not publish that figure.

The Caltrans Highway Design Manual is the clearest single statement of the range: vertical curbs "vary in height from 4 inches to 8 inches" at a batter of about 1:4, sloped curbs "vary in height from 3 inches to 6 inches" at 2:3 or flatter, and curb should be avoided altogether at posted speeds of 40 mph or more. Iowa SUDAS puts it in one sentence: "typically, a curb should be 6 inches high, 6 inches wide." For the full dimension picture, including top width, reveal and batter, see our standard curb dimensions reference.

The federal range, and why it is wider than most articles say

There is only one curb height written into federal law, and it is a definition rather than a limit. The 2023 Public Right-of-Way Accessibility Guidelines define "standard curb height" in R104.3 as "the typical height of a curb according to local standards for a given road type, but usually between 3 inches (75 mm) and 9 inches (230 mm) high relative to the surface of the roadway or gutter."

Read that carefully, because the phrasing is doing a lot of work. It is describing what curbs happen to be, not setting a floor or a ceiling. Nothing in PROWAG, and nothing in the 2010 ADA Standards, sets a minimum or maximum curb height at all. So when an article tells you a curb "must be" 6 inches, or that there is a legal maximum, it is wrong on both counts. The only federal number is this 3 to 9 inch range, it is explicitly tied to "local standards for a given road type," and anything narrower than that range is somebody's city or state drawing, which always overrides a general figure.

Why six inches is the convention

No agency explains the figure. Caltrans, TxDOT, NJDOT, WSDOT, Iowa SUDAS, MoDOT and NCHRP 537 all specify 6-inch curbs without a sentence of justification. What they do publish are the constraints that bracket it from both sides.

Below 6 inches a curb becomes mountable, which TxDOT treats as a design decision rather than an accident: a mountable face is "less than 6-in in height," and heights of 4 inches or less are preferred because "higher curbs may drag the underside of some vehicles." Above 6 inches the curb becomes a vehicle hazard, which is why Caltrans restricts its 8-inch variants to 35 mph and under and NJDOT caps the face at 4 inches above 40 mph.

The only published reason for 6 specifically is about resurfacing. NJDOT, writing about bridges with sidewalk, says "the desirable curb height should be 6 inches to accommodate future resurfacing." Its ordinary street answer is 4 inches, with "where sidewalks are to be constructed, a 6 inch face may be used." So the honest version is that 6 inches is convention sitting where three published constraints cross: tall enough to stop being mountable, short enough to stay off the high-speed guidance, with two inches of future overlay in hand.

Heights chosen for a behavior, not a load

A good share of published curb heights were chosen for what they make a driver do, not for anything structural. A curb is tall where an agency wants to deter parking, short where it has to sit under a guardrail, and shorter still where a truck needs to track over a roundabout island.

The guardrail case is the one worth understanding, because it is a safety rule and it gets misquoted constantly. NCHRP Report 537 quotes the AASHTO Green Book in full: "if a curb is used in conjunction with a traffic barrier, the height of a vertical curb should be limited to 100 mm or it should be of the sloping type." The opening clause gets cut almost everywhere the sentence is repeated, which makes it look as though every 6-inch curb in the country is twice the allowed height. It is not. MoDOT applies it exactly as written, "when curbs are constructed directly beneath guardrail the curb height will be 4 inches," and publishes 6-inch and taller curb everywhere else.

Can a car drive over it? Three states, three answers

Mountability sounds like it has a yes or no answer, and the published thresholds do not agree. TxDOT calls a curb mountable if the face is "less than 6-in in height." WSDOT says vertical curbs "more than 4 inches tall are not considered mountable," while "sloping face curbs as tall as 6 inches are mountable." NJDOT says that "for new installations of sloping curb, the overall curb height shall not exceed 4 inches."

Run a 5-inch vertical curb past all three and it is mountable in Texas, not mountable in Washington, and not buildable in New Jersey. Same concrete, same physics, three published numbers. Our mountable curb guide goes through which definition applies where, and the heights DOTs publish for the rolled profile.

Street, sidewalk, and parking curb heights

Street curb. The 6-inch figure above is the street curb height. On a faster or arterial road it can run to 8 inches, and on a residential street it is often dropped to a 4-inch mountable profile so residents can cross it into a driveway.

Sidewalk curb. A sidewalk curb is just the street curb with a sidewalk behind it, so it stands at the usual street height of about 6 inches. The sidewalk itself is a different measurement: it is a thickness, not a curb height, and cities commonly specify a 4-inch sidewalk slab. Centralia, Washington, for example, specifies sidewalks 4 inches thick. Where a sidewalk meets a crossing the curb drops to flush at an ADA curb ramp, covered in our types of curbs guide.

Parking curb (wheel stop). A precast parking curb, or wheel stop, is short on purpose. Published dimensions settle around a 5-1/4 by 7-1/2 inch section, and where a city fixes the height it is low: Milford, Ohio specifies a wheel stop "6 in high by 6 in wide by 8 ft long," and Wilmington, North Carolina caps a vertical curb used as a wheel stop at a maximum 4 inches high. The full dimensions, weights and anchoring are on our precast concrete curb guide.

Finding the height on your own drawing

Every figure here comes from somebody's standard detail, and yours is probably published too. Search for your city name plus "standard details," or your state DOT plus "standard plans," and look for the curb and gutter sheet. One caution when you read it: the height on the sheet is usually the full section, not the reveal. A curb with a 6-inch reveal above the gutter often has several more inches buried, so NJDOT's 9 by 16 inch vertical curb is a full square foot of concrete even though a pedestrian sees 7 or 8 inches of it. Enter the concrete you are pouring, not the step you can see, and the concrete curb calculator turns it into cubic yards and bags.