# Egress Width Calculator: Stairs, Doors and Corridors under the IBC

> How to size means of egress under IBC Section 1005 — the per-occupant width factors, the sprinkler reduction, the absolute minimums that usually govern, and how width is distributed between exits.

- Canonical: https://harth.build/resources/calculators/egress-width-calculator/
- Last updated: 2026-09-07
- Data source: Method from International Building Code Section 1005 (means of egress sizing), Section 1005.5 (distribution of minimum width), Section 1010 (doors), Section 1011 (stairways) and Section 1020 (corridors), as published in the 2018 and 2021 editions. Minimum dimensions are quoted with their section numbers so each can be checked directly. Confirm every value against the edition adopted by your jurisdiction through the [ICC code library](https://codes.iccsafe.org/codes); the authority having jurisdiction controls.

## Key facts

| Fact | Value |
| --- | --- |
| Stairways | 0.3 in per occupant (IBC §1005.3.1, unsprinklered) |
| Other egress components | 0.2 in per occupant (IBC §1005.3.2, unsprinklered) |
| Sprinklered with voice alarm | 0.2 in stairs / 0.15 in other (requires NFPA 13 or 13R system plus emergency voice/alarm) |
| Minimum corridor width | 44 in (IBC §1020.2, with narrower exceptions) |
| Minimum door clear width | 32 in (IBC §1010.1.1, measured at 90 degrees open) |
| Capacity in any one exit | ≤ 50% of the total required (IBC §1005.5) |

## Direct answer

Egress width under the IBC is a multiplication, then a comparison. Section 1005.3.1 requires stairway capacity of 0.3 inches per occupant and Section 1005.3.2 requires 0.2 inches per occupant for every other egress component — doors, corridors, ramps. Where the building is sprinklered throughout in accordance with Section 903.3.1.1 or 903.3.1.2 and fitted with an emergency voice/alarm communication system, those factors reduce to 0.2 and 0.15 respectively. The calculated figure is then compared against the absolute minimum dimensions elsewhere in Chapter 10: a 44-inch corridor, a 44-inch stairway, a 32-inch clear door opening. In most buildings under a few hundred occupants the absolute minimum is larger than the calculated width and therefore governs. Section 1005.5 then prevents the total from being concentrated in one place: no single exit may carry more than half the required capacity.

*Content and cited inputs reviewed by [Scott Barrington](https://nz.linkedin.com/in/barrington), Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.*


![Labeled code-calculation diagram: Egress Width Calculator: Stairs, Doors and Corridors under the IBC](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/calculators/egress-width-calculator/diagram-1344.webp)

*How to size means of egress under IBC Section 1005 — the per-occupant width factors, the sprinkler reduction, the absolute minimums that usually govern, and…*

## What must be verified before using this guidance?

IBC Section 1005.3 sizes egress components by capacity per occupant:

| Component | Unsprinklered | Sprinklered throughout **and** emergency voice/alarm |
| --- | --- | --- |
| Stairways (§1005.3.1) | 0.3 in per occupant | 0.2 in per occupant |
| All other egress components (§1005.3.2) | 0.2 in per occupant | 0.15 in per occupant |

"All other egress components" means doors, corridors, ramps, aisles and exit passageways. The reduced factors require **both** the sprinkler system (per §903.3.1.1 or §903.3.1.2) and the emergency voice/alarm communication system (per §907.5.2.2). One without the other does not qualify.

## Then check the absolute minimums

The calculated capacity is a floor, not the answer. Compare it against the fixed dimensions in Chapter 10 and take the larger:

| Element | Minimum | Section |
| --- | --- | --- |
| Door clear opening width | 32 in, measured with the door open 90° | §1010.1.1 |
| Corridor width | 44 in (narrower where serving an occupant load under 50, and other exceptions) | §1020.2 |
| Stairway width | 44 in (36 in where serving an occupant load under 50) | §1011.2 |
| Ramp width | 44 in | §1012.5.1 |
| Headroom, stairways | 80 in | §1011.3 |

In a building of a few hundred occupants the minimum dimension almost always governs, which is why experienced reviewers check the minimums first and the arithmetic second.

## Worked example: a 480-occupant floor

A storey with an occupant load of 480, sprinklered throughout with an emergency voice/alarm system, exiting through two stairs and two exit-access doors.

**Stairways** — 480 × 0.2 = **96 inches** of total stair width required.

Section 1005.5 caps any single exit at half the required capacity, so each of the two stairs must carry at least 96 ÷ 2 = 48 inches. A 48-inch clear stair width each is therefore the minimum, and it exceeds the 44-inch absolute minimum, so **the calculation governs here**.

**Doors and corridors** — 480 × 0.15 = **72 inches** total, distributed so that no single doorway carries more than 36 inches. A pair of doors with 36 inches clear each satisfies both the capacity and the 32-inch minimum.

Now drop the same floor to 120 occupants: stairs need 120 × 0.2 = 24 inches total, doors need 18 inches. Both are below the absolute minimums, so the building is designed to 44-inch stairs and 32-inch clear doors and the arithmetic never binds.

## Where width is measured, and what may project into it

Required width is **clear** width. Section 1005.7 permits limited projections: handrails may project up to 4.5 inches on each side into the required stair width, and doors in any position may not reduce the required width by more than half, nor project more than 7 inches into the required width when fully open. Everything else — trim, columns, wall-mounted equipment — comes out of the clear dimension.

## The order to work in

1. Fix the **occupant load** for the storey, function by function.
2. Confirm whether the building qualifies for the **reduced factors** (sprinklers *and* voice/alarm).
3. Calculate total required width for stairs and for other components.
4. Apply the **50 percent distribution rule** to get the per-exit requirement.
5. Compare each result against the **absolute minimum** and take the larger.
6. Deduct **projections** to confirm the clear dimension survives detailing.

## Egress width worksheet

| Step | Input | Value |
| --- | --- | --- |
| 1 | Storey occupant load | |
| 2 | Sprinklered per §903.3.1.1 or §903.3.1.2? | Yes / No |
| 3 | Emergency voice/alarm per §907.5.2.2? | Yes / No |
| 4 | Stair factor (0.3, or 0.2 if both above are yes) | |
| 5 | Other-component factor (0.2, or 0.15 if both above are yes) | |
| 6 | Total stair width required = (1) × (4) | |
| 7 | Total other width required = (1) × (5) | |
| 8 | Number of exits provided | |
| 9 | Minimum per-exit stair width = (6) ÷ 2 (§1005.5 cap) | |
| 10 | Governing stair width = greater of (9) and 44 in | |
| 11 | Governing door clear width = greater of (7) ÷ 2 and 32 in | |
| 12 | Governing corridor width = greater of (7) and 44 in | |
| 13 | Projections deducted (handrails, doors, trim) | |
| 14 | Clear width achieved on the drawing | |

**Record with the calculation:**

| Item | Entry |
| --- | --- |
| Adopted IBC edition and effective date | |
| Local amendments to Chapter 10 | |
| Occupant load source (calculation, fixed seats, AHJ increase) | |
| Accessible means of egress checked separately (§1009)? | |
| Reviewer and date | |

**This worksheet records a calculation, not a compliance determination.**

## Where can you explore related guidance?

- [Explore all calculators guidance](https://harth.build/resources/calculators.md)
- [Occupant Load Calculator: IBC Method, Factors and Worked Example](https://harth.build/resources/calculators/occupant-load-calculator.md)
- [Exit Access Travel Distance: IBC Limits, Measurement and Common Path](https://harth.build/resources/calculators/exit-access-travel-distance-calculator.md)
- [Allowable Height and Area Calculator: IBC Chapter 5 Method](https://harth.build/resources/calculators/allowable-height-and-area-calculator.md)
- [Plumbing Fixture Count Calculator: IBC Table 2902.1 Method](https://harth.build/resources/calculators/plumbing-fixture-count-calculator.md)

## Sources and method

Method from International Building Code Section 1005 (means of egress sizing), Section 1005.5 (distribution of minimum width), Section 1010 (doors), Section 1011 (stairways) and Section 1020 (corridors), as published in the 2018 and 2021 editions. Minimum dimensions are quoted with their section numbers so each can be checked directly. Confirm every value against the edition adopted by your jurisdiction through the [ICC code library](https://codes.iccsafe.org/codes); the authority having jurisdiction controls.

### Source links

- [codes.iccsafe.org](https://codes.iccsafe.org/codes)

## Frequently asked questions

### Does a sprinkler system always reduce the required egress width?

No — the reduction needs two things, not one. IBC Section 1005.3.1 and 1005.3.2 allow the reduced factors only where the building is sprinklered throughout in accordance with Section 903.3.1.1 or 903.3.1.2 *and* is provided with an emergency voice/alarm communication system in accordance with Section 907.5.2.2. A sprinklered building without the voice/alarm system does not qualify.

### Why does my calculated egress width come out smaller than the door I have to install?

Because at low occupant loads the calculation is not what governs. A 60-occupant floor needs 60 × 0.2 = 12 inches of door width, which is far less than the 32-inch clear width Section 1010.1.1 requires anyway. Egress width is the larger of the calculated capacity and the absolute minimum dimension — and in most small and mid-sized buildings the minimum wins.

### Can one wide stair carry all the required capacity?

No. Section 1005.5 requires the required capacity to be distributed so that the loss of any one exit or exit-access doorway leaves at least half the required capacity available. In practice that means no single exit may be credited with more than 50 percent of the total required width, which is what forces genuinely remote second stairs rather than a token one.

### Which occupant load do I use for a stair serving several floors?

Under Section 1005.3.1 the stair is sized for the occupant load of the storey it serves that produces the largest requirement, considering each storey individually rather than summing every floor above. Section 1006.3.1 makes the same point for exit count. Convergence — where an upper and a lower flight arrive at the same point — is handled separately in Section 1005.6.

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