# Tread Depth and Risers
### Stair tread depth and riser height code
**Residential stair code** sets two core dimensions under **IRC 2021 Section R311.7.5**. The **minimum stair tread depth** is **10 inches**. The **maximum stair riser height** is **7 3/4 inches**.
These rules define the baseline for **stair tread depth code**, **stair riser code**, and overall **IRC stair dimensions**. They also work with the **3/8-inch uniformity rule** and the **nosing requirements** for residential stairs.
### Stair tread and riser code at a glance
| Requirement | IRC rule |
| --------------------------------------- | ---------------------------- |
| Minimum tread depth | **10 in.** |
| Maximum riser height | **7 3/4 in.** |
| Maximum tread variation in one flight | **3/8 in.** |
| Maximum riser variation in one flight | **3/8 in.** |
| Nosing projection | **3/4 in. to 1 1/4 in.** |
| Maximum nosing radius | **9/16 in.** |
| Maximum bevel | **1/2 in.** |
| Nosing not required when tread depth is | **11 in. or more** |
| Maximum riser slope | **30 degrees from vertical** |
### What is the minimum stair tread depth?
Under **IRC R311.7.5.2**, the **minimum stair tread depth** is **10 inches**. This is the standard number most people mean when they search for **stair tread depth code** or **residential stair tread depth**.
The code measures tread depth horizontally. Measure between the foremost projections of adjacent treads at a right angle to the leading edge.
Within one flight, the deepest and shallowest treads cannot vary by more than **3/8 inch**. A stair can fail inspection even when every tread is at least **10 inches** if the flight is not uniform.
### What is the maximum stair riser height?
Under **IRC R311.7.5.1**, the **maximum stair riser height** is **7 3/4 inches**. This is the main number behind searches for **stair riser height code** and **maximum riser height for residential stairs**.
Riser height is measured vertically between the leading edges of adjacent treads. The IRC does not set a minimum riser height, but it does require consistency.
Within one flight, the tallest and shortest risers cannot vary by more than **3/8 inch**. Risers may also be vertical or sloped no more than **30 degrees from vertical**.
### Why the 3/8-inch stair uniformity rule matters
The **3/8-inch rule** applies separately to **tread depth**, **riser height**, and **nosing projection**. It is one of the most common residential stair code failures.
Uniform stairs are safer to use. Even small changes in step geometry increase trip risk because people expect each step to match the previous one.
### Stair nosing requirements
Under **IRC R311.7.5.3**, stairs usually need a **nosing**. The nosing must:
* project **3/4 inch to 1 1/4 inches**
* have a radius no greater than **9/16 inch**
* have a bevel no greater than **1/2 inch**
* stay uniform within **3/8 inch** across the flight
A nosing is **not required** when the tread depth is **11 inches or more**. That exception is important when comparing **10-inch tread code** with deeper custom stair layouts.
### How to measure stair tread depth and riser height
Use this sequence when checking **stair dimensions** for code compliance:
1. Measure each **riser height** vertically between adjacent tread leading edges.
2. Measure each **tread depth** horizontally from leading edge to leading edge.
3. Compare all risers in the flight for the **3/8-inch** maximum variation.
4. Compare all treads in the flight for the same **3/8-inch** maximum variation.
5. Confirm the nosing profile meets the required projection and shape limits.
### Related stair code conditions
Some stair layouts have added rules beyond standard **tread depth and riser height**:
* **Open riser stairs** must meet the **4-inch sphere rule** once the stair is more than **30 inches** above the floor or grade below. See [Open Riser Code Requirements](/code-compliance/stair-code/open-riser-code-requirements.md).
* **Winder stairs** must provide at least **10 inches** at the walkline and **6 inches** at the narrowest point. See [Winder Staircase Code Requirements](/code-compliance/stair-code/winder-staircase-code-requirements.md).
* Stairs with **4 or more risers** need a handrail. See [When is Handrail Required?](/code-compliance/getting-started/when-is-handrail-required.md).
### Frequently asked questions
What is the minimum tread depth for residential stairs?
The **minimum tread depth** is **10 inches** under **IRC R311.7.5.2**. Measure it horizontally between adjacent tread leading edges.
What is the maximum riser height for stairs?
The **maximum riser height** is **7 3/4 inches** under **IRC R311.7.5.1**. Risers in the same flight must also stay within **3/8 inch** of each other.
Do stairs need a nosing?
Usually yes. Under **IRC R311.7.5.3**, a nosing is generally required unless the tread depth is **11 inches or more**.
What does the 3/8-inch stair rule mean?
The largest and smallest **riser heights**, **tread depths**, or **nosing projections** in one flight cannot differ by more than **3/8 inch**. The rule applies to each dimension separately.
### Related pages
* [Open Riser Code Requirements](/code-compliance/stair-code/open-riser-code-requirements.md)
* [Winder Staircase Code Requirements](/code-compliance/stair-code/winder-staircase-code-requirements.md)
* [When is Handrail Required?](/code-compliance/getting-started/when-is-handrail-required.md)
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