Fixture Unit Calculator

Total WSFU from IPC 2021 Table E103.3(2) and DFU from Table 709.1 — then take each number to the calculator that actually uses it

The other four plumbing calculators on this hub ask for a fixture-unit total you were supposed to already know. This one builds that total from a real fixture list. You get two answers, not one: water-supply fixture units and drainage fixture units. They are different code systems. Do not mix them.

How the units work: fixture unit guide. Counting mistakes: troubleshooting. Group vs pieces: bathroom group vs individual counting. Lookup table: fixture unit chart. Then: supply pipe, vent, slope, water heater. Plumbing index: plumbing calculators hub.

Basement groundwater is a different worksheet: Sump Pump Sizing Calculator (basin, inflow GPM, total head — starting point, not a named-model pump curve).

Prescriptive starting point only — two separate totals from two separate IPC tables, not a substitute for the plumbing code your city adopted. Water-supply fixture units (WSFU) come from 2021 International Plumbing Code Table E103.3(2), private occupancy, Total column (Colorado / Connecticut IPC 2021 on UpCodes). Drainage fixture units (DFU) come from IPC 2021 Table 709.1. They are not the same number and they do not go into the same calculator. Hose bibbs are not in Table E103.3(2); IPC Appendix E treats them as continuous gpm. UPC Table 610.3 (Hawaii Plumbing Code 2021) assigns 2.5 WSFU to the first hose bibb. Public occupancy, flushometer batteries, and unlisted fixtures need the code book, not this residential list. Not a permit.

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How to Use This Fixture Unit Calculator

Count bathroom groups first if the rooms qualify (water closet + lavatory + tub or shower, same floor). Then add kitchen, dishwasher, clothes washer, and anything that is not inside a group. Calculate. You get two numbers. The WSFU total goes to the water supply pipe sizing calculator. The DFU total goes to the DWV vent sizing calculator, and after diameter is set, the drain pipe slope calculator sets the fall. Why they differ: fixture unit guide. Side-by-side table: fixture unit chart.

WSFU = Σ Table E103.3(2) Total · DFU = Σ Table 709.1 · do not add a bathroom group and its pieces

What These Numbers Are (and Are Not)

The WSFU total is the private-occupancy Total column from Table E103.3(2) for the fixtures you typed. It is the number the supply-pipe calculator wants. The DFU total is Table 709.1 for those same fixtures. It is the number the vent calculator wants. Neither one is first-hour rating. The water heater sizing calculator still wants people, baths, and peak hour.

Hose bibbs

They are on the list because people forget them, and because UPC Table 610.3 actually assigns 2.5 WSFU (1.0 each additional). They are not on IPC Table E103.3(2). Appendix E says constant-use fixtures get gpm, not fixture units. The results panel keeps that add-on on its own line so an IPC walk and a UPC walk stay honest.