How to use the plumbing fixture calculator
Restroom counts drive a surprising amount of a floor plan. They fix the size of the core, the number of wet walls and where risers can go, so it pays to know the number early rather than after the layout is frozen. In most of the United States the minimum count comes from the International Plumbing Code, Table 2902.1, which the IBC repeats in Chapter 29. This calculator applies that table for the most common occupancies.
- Choose the occupancy classification of the space, the same one you use for egress and fire separation.
- Enter the occupant load. Use the design occupant load from IBC Chapter 10, which our occupancy load calculator works out from floor area and use.
- Set the split between women and men. The code default is 50/50; change it only where your jurisdiction accepts a documented split.
- Choose whether to use urinals to see how many water closets in the men's room can be swapped for urinals.
- Read the counts for each restroom, the total drinking fountains and service sinks, and the notes on separate facilities.
How the fixture count is calculated
Occupants per sex = total occupant load × share, rounded up
Water closets per sex = occupants ÷ ratio, rounded up
Lavatories per sex = occupants ÷ ratio, rounded up
Drinking fountains = total occupants ÷ ratio, rounded up
Urinals may replace up to 67% of men's water closets (assembly, educational) or 50% (other occupancies)
Some occupancies use a stepped ratio. Business occupancies need 1 water closet per 25 for the first 50 people and 1 per 50 after that, and 1 lavatory per 40 for the first 80 and 1 per 80 after that. Arenas and stadiums step down once a restroom serves more than about 1,500 people. The calculator applies these steps for you.
| Occupancy | Water closets | Lavatories | Drinking fountains |
|---|---|---|---|
| B: Business | 1 per 25 for first 50, then 1 per 50 | 1 per 40 for first 80, then 1 per 80 | 1 per 100 |
| A-2: Restaurants | 1 per 75 | 1 per 200 | 1 per 500 |
| A-2: Nightclubs, bars | 1 per 40 | 1 per 75 | 1 per 500 |
| A-1: Theatres | Men 1 per 125, women 1 per 65 | Men 1 per 200, women 1 per 150 | 1 per 500 |
| E: Educational | 1 per 50 | 1 per 50 | 1 per 100 |
| M: Mercantile | 1 per 500 | 1 per 750 | 1 per 1,000 |
| S: Storage | 1 per 100 | 1 per 100 | 1 per 1,000 |
Worked examples
An office floor of 200 people
Split 50/50 gives 100 men and 100 women. Water closets per sex are 50 ÷ 25 = 2 for the first 50, plus 50 ÷ 50 = 1 for the rest, so 3 each. Lavatories are 80 ÷ 40 = 2, plus 20 ÷ 80 rounded up to 1, so 3 each. The floor needs 2 drinking fountains and 1 service sink. In the men's room, up to half of the 3 water closets can be urinals, so 2 water closets and 1 urinal work.
A 150-seat restaurant
With 75 men and 75 women, each restroom needs 75 ÷ 75 = 1 water closet and 75 ÷ 200 rounded up to 1 lavatory. One drinking fountain and one service sink complete the count. Many restaurants put the drinking fountain requirement on a water station where the local code allows it.
A 600-seat theatre
Women need 300 ÷ 65 = 4.6, so 5 water closets, while men need 300 ÷ 125 = 2.4, so 3. Lavatories are 2 for women and 2 for men. Because theatres are an assembly occupancy, up to 67 percent of the men's water closets can be urinals, so 1 water closet and 2 urinals meet the minimum. Most theatre designers add more than the minimum because intervals create queues.
Who this calculator helps
- Architects sizing cores, restrooms and wet walls at concept and schematic design.
- Interior designers planning tenant fit-outs, restaurants and offices where the restroom count limits the layout.
- MEP and plumbing engineers checking fixture counts before sizing drainage and water supply.
- Developers and project managers testing whether a change of use will need new restrooms.
- Restaurant and retail operators checking how many seats an existing restroom can support.
- Students learning how the plumbing code ties into occupancy and egress.
Practical tips
- Use the same occupant load for plumbing that you use for egress, unless your code allows a separate plumbing occupant load.
- In a multi-tenant building, required facilities can often be shared if they are within the travel distance limit, usually 500 ft (152 m), and on the same floor or one floor away.
- Accessible toilet rooms need space; check turning circles and clear floor space with the furniture clearance guide and room sizes with the square footage calculator.
- Assembly and mercantile buildings with six or more water closets in total usually need a family or assisted-use toilet room as well.
- Check the local plumbing code early; state codes and the UPC can change the ratios and the urinal rules.
Planning a restroom refresh? Show the client finishes and fixtures before they are ordered with Room Redesign.
