What is the maximum nosing projection allowed by code?

The IRC allows a nosing projection between 3/4 inch and 1 1/4 inches (R311.7.5.3). Anything larger becomes a trip hazard rather than extra tread depth.

How much can nosing projections vary between treads?

The IRC requires nosing projection to be uniform: the greatest projection in a flight cannot exceed the smallest by more than 3/8 inch. Measure every tread and shim or re-cut the outliers.

Does nosing count toward tread depth?

Yes. The effective tread depth the code regulates is the horizontal distance from nosing to nosing, which equals the tread board depth plus the nosing projection. The IRC minimum effective depth is 10 inches.

Can I add nosing strips to existing stairs?

Yes. Retrofit nosing strips in aluminum, brass, rubber, or vinyl mount over the existing tread edge, and many include abrasive anti-slip inserts. They are a practical fix for worn, shallow, or slippery nosings.

What nosing material is best?

For high-traffic stairs, aluminum with an abrasive insert balances durability and slip resistance. Brass wears beautifully in visible locations but costs more. Rubber and vinyl are quieter and grippier, making them good for interior retrofits.

Nosing Calculator

What Is the Nosing Calculator?

Stair nosing is the front edge of each tread, the small projection that overhangs the riser below it. It looks like a minor trim detail, but it sets your effective tread depth, catches the ball of your foot on every step down, and is one of the first things an inspector checks. This calculator works out your nosing projection, your effective tread depth (tread board depth plus nosing), and whether both fall inside the code limits, so you can size nosing before you cut a single tread. The International Residential Code (IRC R311.7.5.3) allows a nosing projection between 3/4 inch and 1 1/4 inches, and it requires nosing to be uniform enough that the greatest and smallest projections in a flight differ by no more than 3/8 inch. For accessible commercial stairs, ADA 504.5 goes further: the nosing edge must be curved or beveled with a radius no greater than 1/2 inch, and the underside of the nosing must not be abrupt. Nosing also matters after construction. Retrofit nosing strips in aluminum, brass, rubber, or vinyl, many with abrasive anti-slip inserts, can bring a worn or slippery stair up to a safer standard without replacing the treads, and low-voltage LED nosing profiles add visibility for night use. Enter your tread depth and projection below to check the numbers.

How to Use This Calculator

Measure the actual tread board depth, the flat surface of the tread from the riser face to the front edge of the board, and enter it.
Enter the nosing projection, how far the front edge of the tread overhangs the riser face below it.
Read the effective tread depth, which is the tread board depth plus the nosing projection, the usable surface your foot actually steps on.
Check the effective depth against the IRC minimum of 10 inches, measured horizontally from nosing to nosing.
Check the projection itself against the code band of 3/4 inch minimum to 1 1/4 inches maximum.
Repeat the measurement on every tread and confirm the greatest and smallest projections differ by no more than 3/8 inch, the IRC uniformity limit.

Nosing Calculator