Formulas

WSFU to GPM Conversion Tables

IPC Table E103.3(3) WSFU-to-GPM conversion for flush tank and flushometer systems.

Introduction

The conversion from Water Supply Fixture Units (WSFU) to flow rate (GPM) is non-linear due to diversity factor. IPC Table E103.3(3) provides separate conversion curves for flush tank and flushometer systems.

IPC Table E103.3(3) - Flush Tank System

WSFU	GPM	WSFU	GPM	WSFU	GPM
1	3	20	19	200	60
2	5	30	23	300	75
3	7	40	27	400	85
5	9	50	30	500	95
10	14	70	35	750	115
15	17	100	43	1000	125
20	19	150	53	2000	180

IPC Table E103.3(3) - Flushometer Valve System

WSFU	GPM	WSFU	GPM	WSFU	GPM
1	3	20	27	200	80
2	5	30	33	300	100
3	7	40	38	400	115
5	9	50	43	500	130
10	14	70	50	750	155
15	18	100	60	1000	170
20	27	150	70	2000	225

Notes

• Flushometer systems produce higher peak flow rates than flush tank systems for the same WSFU.
• The conversion is non-linear: 100 WSFU does not equal 100x the flow of 1 WSFU.
• For intermediate values, Plumbing Booster interpolates between table entries.
• These tables are built into the software and applied automatically based on system type.

WSFU Calculation Guide

Understanding WSFU is fundamental to plumbing design. This guide explains what WSFU are, how different codes define them, and how Plumbing Booster uses them for pipe sizing.

IPC Pipe Sizing Guide

Step-by-step explanation of the IPC table-based pipe sizing method, from WSFU summation through flow conversion to final pipe selection using Table E104.1.

Domestic Water Demand Calculation

Domestic water demand calculation is the foundation of plumbing system design. This guide covers WSFU summation, diversity factors, and code-specific flow conversion.