# Plumbing Fixture Count Calculator: IBC Table 2902.1 Method

> How to size plumbing fixtures from the occupant load under IBC Chapter 29 — the ratio structure, the 50/50 gender split default, rounding, and the single-user and family restroom rules.

- Canonical: https://harth.build/resources/calculators/plumbing-fixture-count-calculator/
- Last updated: 2026-09-07
- Data source: Method from International Building Code Chapter 29 — Section 2902.1 and Table 2902.1 (minimum number of required plumbing fixtures), Section 2902.1.1 (fractional numbers), Section 2902.2 (separate facilities) and Section 2902.3 (required public toilet facilities) — as published in the 2018 and 2021 editions, which reference the International Plumbing Code. Only the Group B row is worked through in full, because the table's ratios differ sharply between occupancies and an abridged copy would invite the wrong row to be used. Many jurisdictions enforce the Uniform Plumbing Code instead, whose ratios differ. Confirm the governing code and table through the [ICC code library](https://codes.iccsafe.org/codes) and the state adoption record at [iccsafe.org/adoptions](https://www.iccsafe.org/adoptions); the authority having jurisdiction controls.

## Key facts

| Fact | Value |
| --- | --- |
| Input | Occupant load from IBC Chapter 10 (the same figure used for egress) |
| Gender split | 50 / 50 unless the use indicates otherwise (IBC §2902.2) |
| Group B water closets | 1 per 25 for the first 50, then 1 per 50 (IBC Table 2902.1, 2018/2021) |
| Group B lavatories | 1 per 40 for the first 80, then 1 per 80 (IBC Table 2902.1, 2018/2021) |
| Rounding | Fractions round up (IBC §2902.1.1) |
| Service sink | 1 required (in most occupancies, per Table 2902.1) |

## Direct answer

Plumbing fixture counts under IBC Chapter 29 start from the occupant load calculated under Chapter 10, not from a separate figure. Table 2902.1 then gives a ratio per occupancy for water closets, lavatories, drinking fountains, bathtubs or showers and service sinks. Section 2902.2 requires separate facilities for each sex in most occupancies, and the occupant load is divided equally between the sexes unless statistics for the specific use indicate a different distribution. Fractional fixtures are rounded up under Section 2902.1.1, and the ratios are often stepped rather than linear — Group B water closets are one per 25 for the first 50 occupants and one per 50 for the remainder, so the arithmetic is done in bands rather than by a single division. Occupancy-specific exceptions for small occupant loads, single-user facilities and family or assisted-use rooms then modify the result.

*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: Plumbing Fixture Count Calculator: IBC Table 2902.1 Method](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/calculators/plumbing-fixture-count-calculator/diagram-1344.webp)

*How to size plumbing fixtures from the occupant load under IBC Chapter 29 — the ratio structure, the 50/50 gender split default, rounding, and the single-use…*

## What must be verified before using this guidance?

IBC Section 2902.1 requires plumbing fixtures in at least the number set by **Table 2902.1**, calculated from the **occupant load determined under Chapter 10**. There is no separate plumbing occupant load, which is why the occupant-load calculation is worth getting right once rather than twice.

The table gives, per occupancy group:

- water closets (with separate male and female ratios in the assembly groups);
- lavatories;
- bathtubs or showers, where applicable;
- drinking fountains;
- service sinks.

## The three rules that shape the arithmetic

**1. Split the occupant load.** Section 2902.2 requires separate facilities for each sex in most occupancies, and the occupant load is divided **equally between the sexes** unless statistics for the specific use indicate a different distribution.

**2. Work the bands in order.** Most ratios are stepped, not linear. "1 per 25 for the first 50 and 1 per 50 for the remainder" is three arithmetic steps, not one division.

**3. Round up.** Section 2902.1.1 requires fractional fixtures to be rounded to the next whole number.

## Worked example: a 200-occupant Group B floor

Occupant load 200, split 100 male and 100 female. Ratios from **Table 2902.1 of the 2018/2021 IBC**, Business row.

### Water closets — 1 per 25 for the first 50, then 1 per 50

Per sex, from 100 occupants:

| Band | Occupants in band | Ratio | Fixtures |
| --- | --- | --- | --- |
| First 50 | 50 | 1 per 25 | 2 |
| Remainder | 50 | 1 per 50 | 1 |
| **Per sex** | | | **3** |
| **Total** | | | **6** |

Compare that with the two shortcuts: dividing 100 by 25 gives 4 per sex (over by a third), and dividing 100 by 50 gives 2 per sex (under by a third). Neither shortcut is close.

### Lavatories — 1 per 40 for the first 80, then 1 per 80

| Band | Occupants in band | Ratio | Fixtures |
| --- | --- | --- | --- |
| First 80 | 80 | 1 per 40 | 2 |
| Remainder | 20 | 1 per 80 | 0.25 → **1** |
| **Per sex** | | | **3** |
| **Total** | | | **6** |

The rounding rule earns its keep here: 20 occupants in the second band produce a quarter of a fixture, and a quarter of a fixture is one fixture.

### The rest

| Fixture | Requirement | Result |
| --- | --- | --- |
| Drinking fountains | 1 per 100 occupants | 2 |
| Service sink | 1 | 1 |

**Floor total: 6 water closets, 6 lavatories, 2 drinking fountains, 1 service sink** — before any accessibility, urinal-substitution or travel-distance provision is applied.

## What the count does not settle

A compliant count can still produce a non-compliant building. Check these separately:

- **Accessibility** — at least one of each fixture type in a toilet room must be accessible, and accessible fixtures are counted toward the minimum rather than added to it. ICC A117.1 and the ADA Standards set the clearances.
- **Urinal substitution** — the code permits urinals to be substituted for a proportion of the male water closets, subject to a cap. Read the limit rather than assuming a familiar percentage.
- **Travel distance to toilet facilities** — Section 2902.3.2 limits how far occupants may travel, and on a large floor plate that can force a second core rather than a larger one.
- **Which plumbing code applies** — a UPC jurisdiction uses different ratios entirely.

## The order to work in

1. Take the **occupant load** from the Chapter 10 calculation.
2. Identify the **occupancy row** in Table 2902.1 of the adopted edition.
3. **Split** the load between the sexes.
4. Work each fixture type **band by band**, rounding up at the end of each.
5. Add **drinking fountains** and the **service sink**.
6. Apply the **exceptions** — single-user rooms, small occupant loads, family or assisted-use facilities.
7. Check **accessibility**, **urinal substitution** and **travel distance**.

## Plumbing fixture count worksheet

One worksheet per occupancy per storey. Ratios are read from Table 2902.1 of the adopted edition — this worksheet does not supply them.

| Step | Item | Value |
| --- | --- | --- |
| 1 | Occupancy group | |
| 2 | Occupant load (from Chapter 10 calculation) | |
| 3 | Split — male | |
| 4 | Split — female | |
| 5 | Basis for a non-50/50 split, if used | |

**Water closets**

| Band | Occupants in band | Ratio | Fixtures (round up) |
| --- | --- | --- | --- |
| First band, male | | | |
| Remainder, male | | | |
| First band, female | | | |
| Remainder, female | | | |
| **Total water closets** | | | |

**Lavatories**

| Band | Occupants in band | Ratio | Fixtures (round up) |
| --- | --- | --- | --- |
| First band, male | | | |
| Remainder, male | | | |
| First band, female | | | |
| Remainder, female | | | |
| **Total lavatories** | | | |

**Everything else**

| Fixture | Ratio | Required | Provided |
| --- | --- | --- | --- |
| Drinking fountains | | | |
| Service sinks | | | |
| Bathtubs / showers (where applicable) | | | |
| Urinals substituted (and cap applied) | | | |
| Accessible fixtures within the count | | | |

**Record with the calculation:**

| Item | Entry |
| --- | --- |
| Plumbing code adopted (IPC / UPC / state code) and edition | |
| Local amendments to the fixture table | |
| Exceptions relied on (single-user, small occupant load, family room) | |
| Travel distance to facilities checked (§2902.3.2)? | |
| 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)
- [Egress Width Calculator: Stairs, Doors and Corridors under the IBC](https://harth.build/resources/calculators/egress-width-calculator.md)
- [Allowable Height and Area Calculator: IBC Chapter 5 Method](https://harth.build/resources/calculators/allowable-height-and-area-calculator.md)
- [Exit Access Travel Distance: IBC Limits, Measurement and Common Path](https://harth.build/resources/calculators/exit-access-travel-distance-calculator.md)

## Sources and method

Method from International Building Code Chapter 29 — Section 2902.1 and Table 2902.1 (minimum number of required plumbing fixtures), Section 2902.1.1 (fractional numbers), Section 2902.2 (separate facilities) and Section 2902.3 (required public toilet facilities) — as published in the 2018 and 2021 editions, which reference the International Plumbing Code. Only the Group B row is worked through in full, because the table's ratios differ sharply between occupancies and an abridged copy would invite the wrong row to be used. Many jurisdictions enforce the Uniform Plumbing Code instead, whose ratios differ. Confirm the governing code and table through the [ICC code library](https://codes.iccsafe.org/codes) and the state adoption record at [iccsafe.org/adoptions](https://www.iccsafe.org/adoptions); the authority having jurisdiction controls.

### Source links

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

- [iccsafe.org](https://www.iccsafe.org/adoptions)

## Frequently asked questions

### Which occupant load do I use for fixture counts?

The one calculated under Chapter 10 for the same spaces — there is no separate plumbing occupant load. That is why an occupant-load error propagates: it moves the egress width and the fixture count at the same time. Where the building official has approved an increased occupant load under Section 1004.5.1, the fixture count is calculated at the increased figure too.

### Why does the ratio change part-way through the calculation?

Because most rows in Table 2902.1 are banded rather than linear. The Group B water-closet ratio is one per 25 for the first 50 occupants and one per 50 for everything above that, so a 200-occupant floor is not simply 200 ÷ 25. Dividing straight through by the first-band ratio over-provides; dividing by the second under-provides. Work the bands in order.

### When can a single-user toilet room satisfy the requirement?

Section 2902.2 has exceptions permitting a single facility serving both sexes in small occupancies — for example where the occupant load is low, in specified mercantile and business uses, and in dwelling units. Separately, Section 2902.1.2 allows single-user toilet rooms to be identified for use by all persons. The thresholds are specific and edition-dependent, so read the exception text rather than working from the general rule.

### Does the IBC or the IPC govern my fixture count?

It depends on the jurisdiction. IBC Chapter 29 and IPC Chapter 4 carry the same table and are intended to be read together, but a jurisdiction may adopt the Uniform Plumbing Code instead, whose ratios are structured differently and will give different answers. Confirm which plumbing code your jurisdiction has adopted before you use any table — this is one of the code areas where the IPC/UPC split matters most in practice.

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