Water Supply Fixture Units - WSFU vs. GPM and Liters/sec

The Water Supply Fixture Unit (WSFU) is defined by the American Uniform Plumbing Code (UPC) and is used to calculate the demand in water supply systems.

Key Conversion: 1 WSFU = 1 GPM

This conversion is suitable for single or a few fixtures. When many fixtures are combined, the number must be compensated for intermittent use through probability curves or tables for sizing water supply lines.

Demand in Water Supply System without Flush Valves

Use this table for systems without flush valves to estimate water demand based on WSFU load.

WSFU	GPM	ft³/min	Liters/sec
1	3	0.41	0.19
2	5	0.68	0.32
4	8	1.07	0.51
8	12.8	1.71	0.81
15	17.5	2.3	1.1
30	23.3	3.1	1.5
50	29.1	3.9	1.8

Demand in Water Supply System with Flush Valves

Use this table for systems with flush valves to estimate water demand based on WSFU load.

WSFU	GPM	ft³/min	Liters/sec
5	15	2	1
7	19.8	2.7	1.3
10	27	3.6	1.7
15	31	4.1	2
20	35	4.7	2.2
30	42	4	1.9
50	50	6.7	3.2