Fixture Unit (DFU) Calculator
Drainage Fixture Units (DFUs) are the standard way to calculate drain pipe sizing. This calculator totals your fixtures and recommends drain pipe sizes per IPC code.
Enter Your Measurements
Results
How to Use This Calculator
- Enter the count of each fixture type.
- Review total DFUs and recommended pipe sizes.
- Use the building drain size for the main horizontal drain exiting your foundation.
How Fixture Units Calculation Works
The DFU system standardizes drainage load across different fixture types. Each fixture has an assigned value based on its flow rate and frequency of use. The total DFU determines the minimum pipe sizes for branches, stacks, and the building drain per IPC Table 710.1. Toilets always require a minimum 3" drain regardless of DFU count. Building drains are typically 4" for residential homes (handles up to 180 DFU at 1/8" slope).
Formula
Toilet = 4 DFU, Tub/Shower = 3 DFU, Lav = 1 DFU, Kitchen Sink = 2 DFU, Dishwasher = 2 DFU, Washing Machine = 3 DFU, Floor Drain = 2 DFU. Pipe sizing per IPC Table 710.1.