Class 1 vs Class 2 vs Class 3 Riprap (State DOT System vs Light/Medium/Heavy)

There’s no universal Class 1/2/3 standard — here’s proof

The FAA/Alaska figure and the North Carolina figure describe genuinely different physical stone sizes under the identical label “Class I” — one caps out where the other’s minimum threshold begins. This isn’t an error in any of these specifications; each agency calibrated its own class system to its own typical applications and historical practice.

Light/medium/heavy vs. DOT class systems

This naming describes stone size directly and is useful for general residential and commercial planning where no specific agency spec applies. If your project sits within a jurisdiction or agency that requires a named DOT class, that agency’s own gradation table governs — not this commercial naming, and not another state’s class numbers.

Why the variance exists

Each state DOT (or agency like the FAA) developed its riprap classes around its own typical projects, local rock sources, and historical design practice. A department that mostly specifies riprap for small drainage ditches calibrates its “Class I” around correspondingly small stone. A department focused on larger channel and shoreline work calibrates its lowest class differently. Neither approach is wrong — they’re simply optimized for different typical use cases, which is exactly why the same class number ends up describing different stone across agencies.

Graded vs. uniform classes within DOT systems too

On top of the numbered class variance, many state specs also distinguish graded riprap (a mixed range of sizes, generally preferred for flexibility and self-healing) from uniform riprap (stones close to one consistent size). Indiana’s specification, for example, includes separate “Uniform A” and “Uniform B” gradations alongside its standard revetment classes. This mirrors the general graded-vs-uniform distinction covered in Riprap Size Chart: Light vs Medium vs Heavy, but with its own agency-specific numbers layered on top.

How to actually use a state DOT specification

• Identify the exact governing agencyState DOT, county, FAA, or another authority — each has its own document, not a shared national one.
• Pull the current specification directlyClass definitions get revised over time — don’t rely on an old or secondhand summary.
• Match by weight range, not class number aloneA “Class II” in one state might match a “Class I” or “Class III” in another by actual stone weight — compare the numbers, not just the label.
• Confirm gradation percentages, not just the rangeMost specs require a percentage of stones above or below specific weight thresholds, not just a min-max range.

Converting a DOT class to tonnage

Once you know the actual stone size (D50) and thickness a specific DOT class calls for, the tonnage formula is the same one used throughout our other riprap guides — see How Many Tons of Riprap Do I Need? for the full breakdown.

What to confirm before ordering to a DOT class

• The exact agency and current spec revisionNot a general “Class I” assumption from memory or another state’s document.
• Weight range and percentage requirementsThe full gradation table, not just the class name.
• Required layer thickness for that classOften specified directly in the same table as the weight range.
• Whether graded or uniform gradation is requiredA separate specification choice within many DOT systems.

Three “Class I” calls, three different stone sizes

Example 1 — North Carolina DOT Class 1

Stones 5-200 lb, at least 30% weighing a minimum of 60 lb each — a fairly wide range suited to general erosion control work.

Example 2 — a typical municipal Class I (Virginia-style spec)

Stones 50-150 lb, with 60% weighing over 100 lb — noticeably narrower and, on average, heavier than the NCDOT example above, despite the identical class name.

Example 3 — FAA/Alaska DOT Class I (airport application)

Stones capped at 25 lb for the bulk of the mix, with only 0-10% exceeding 50 lb — dramatically smaller than either of the other two “Class I” examples, reflecting the lighter-duty erosion control typical around airport drainage.

Mistakes with riprap class terminology

• Assuming “Class I” means the same thing everywhereIt can mean stones anywhere from under 25 lb to 200 lb, depending entirely on the specifying agency.
• Using a spec from the wrong agency or an outdated revisionClass definitions are revised over time and vary by jurisdiction — always pull the current, exact document that governs your project.
• Treating a commercial light/medium/heavy label as a DOT class equivalentThese naming systems aren’t interchangeable, even where the general size ranges happen to overlap.
• Ordering by class number alone without checking the weight tableAlways confirm the actual weight range and percentage requirements, not just the class name.
• Ignoring the graded vs. uniform distinction within a specSome DOT systems separate these as distinct requirements alongside the numbered classes.

Quick reference: don’t assume, verify

What determines a specific class’s stone size

• The specifying agencyEach defines its own class system independently — there’s no shared national baseline.
• Typical local applicationsAgencies calibrate classes around the projects they most commonly specify for.
• Spec revision dateClass definitions can change over time within the same agency.
• Graded vs. uniform requirementA separate axis some specs apply alongside the numbered class.

Navigate riprap class terminology in five steps

1. Identify the exact agency whose spec governs your project.
2. Pull the current gradation table directly from that agency.
3. Read the actual weight range and percentages, not just the class name.
4. Don’t cross-reference class numbers between agencies — compare weights instead.
5. Convert the confirmed stone size to tonnage using the standard formula.

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