Fixture Unit Calculator
Pick IPC or UPC and private or public occupancy, enter fixture counts, and get total DFU and WSFU, peak demand in GPM from Hunter's curve, and the minimum building drain, branch, and stack size.
Use the Fixture Unit Calculator
Fixture Schedule
Quantities are kept when you switch code or occupancy.
| Fixture Type | DFU | WSFU | Quantity |
|---|---|---|---|
| Bathroom group (1.6 gpf tank WC, lav, tub/shower) | 5 | 3.6 | |
| Bathtub or tub/shower combination | 2 | 1.4 | |
| Shower (single head, ≤ 5.7 gpm) | 2 | 1.4 | |
| Lavatory | 1 | 0.7 | |
| Water closet, 1.6 gpf flush tank | 3 | 2.2 | |
| Water closet, 1.6 gpf flushometer valve | 3 | 6 | |
| Urinal, ≤ 1 gpf flushometer valve | 2 | — | |
| Kitchen sink (public: restaurant/hotel) | 2 | 1.4 | |
| Dishwasher, domestic | 2 | 1.4 | |
| Clothes washer (8 lb / domestic) | 2 | 1.4 | |
| Laundry tray / laundry sink | 2 | 1.4 | |
| Service or mop sink | 2 | — | |
| Bar sink | 2 | — | |
| Bidet | 1 | 2 | |
| Drinking fountain | 0.5 | — | |
| Floor drain (2 in. trap) | 2 | 0 | |
| Hose bibb | 0 | — |
Enter fixture quantities
and click Calculate.
Total DFU
Drain, waste & vent load
Total WSFU
Water supply load
Estimated peak demand
Minimum drain size for this DFU
Breakdown by fixture
| Fixture | Qty | DFU | WSFU |
|---|
Fixture unit values: IPC vs UPC, private vs public
| Fixture | IPC DFU | IPC WSFU | UPC DFU | UPC WSFU | ||||
|---|---|---|---|---|---|---|---|---|
| Pvt | Pub | Pvt | Pub | Pvt | Pub | Pvt | Pub | |
| Bathroom group (1.6 gpf tank WC, lav, tub/shower) | 5 | — | 3.6 | — | — | — | — | — |
| Bathtub or tub/shower combination | 2 | 2 | 1.4 | 4 | 2 | 2 | 4 | 4 |
| Shower (single head, ≤ 5.7 gpm) | 2 | 2 | 1.4 | 4 | 2 | 2 | 2 | 2 |
| Lavatory | 1 | 1 | 0.7 | 2 | 1 | 1 | 1 | 1 |
| Water closet, 1.6 gpf flush tank | 3 | 4 | 2.2 | 5 | 3 | 4 | 2.5 | 2.5 |
| Water closet, 1.6 gpf flushometer valve | 3 | 4 | 6 | 10 | 3 | 4 | — | — |
| Urinal, ≤ 1 gpf flushometer valve | 2 | 2 | — | 5 | 2 | 2 | — | — |
| Kitchen sink (public: restaurant/hotel) | 2 | 2 | 1.4 | 4 | 2 | 2 | 1.5 | 1.5 |
| Dishwasher, domestic | 2 | 2 | 1.4 | — | 2 | 2 | 1.5 | 1.5 |
| Clothes washer (8 lb / domestic) | 2 | — | 1.4 | 3 | 3 | 3 | 4 | 4 |
| Laundry tray / laundry sink | 2 | 2 | 1.4 | — | 2 | 2 | 1.5 | 1.5 |
| Service or mop sink | 2 | 2 | — | 3 | — | 3 | 1.5 | 3 |
| Bar sink | 2 | 2 | — | — | 1 | — | 1 | 2 |
| Bidet | 1 | 1 | 2 | — | 1 | — | 1 | — |
| Drinking fountain | 0.5 | 0.5 | — | 0.25 | 0.5 | 0.5 | 0.5 | 0.5 |
| Floor drain (2 in. trap) | 2 | 2 | 0 | 0 | 2 | 2 | 0 | 0 |
| Hose bibb | 0 | 0 | — | — | 0 | 0 | 2.5 + 1 ea. | 2.5 + 1 ea. |
- IPC 2021 Table 709.1 rates water closets by private/public use (3 or 4 DFU at 1.6 gpf; 4 or 6 above 1.6 gpf) and urinals above 1 gpf at 4 DFU. Showers above 5.7 gpm rise to 3–6 DFU.
- IPC WSFU are the total-load column of Appendix E Table E103.3(2); separate hot and cold loads are about three-quarters of the total. Appendix E applies only where adopted.
- UPC Table 610.3: hose bibbs are 2.5 WSFU for the first and 1.0 for each additional; flushometer valves are sized under Section 610.10 instead of by WSFU.
IPC drain pipe sizing by DFU
| Pipe (in) | 1/16 | 1/8 | 1/4 | 1/2 |
|---|---|---|---|---|
| 1¼ | — | — | 1 | 1 |
| 1½ | — | — | 3 | 3 |
| 2 | — | — | 21 | 26 |
| 2½ | — | — | 24 | 31 |
| 3 | — | 36 | 42 | 50 |
| 4 | — | 180 | 216 | 250 |
| 5 | — | 390 | 480 | 575 |
| 6 | — | 700 | 840 | 1,000 |
| 8 | 1,400 | 1,600 | 1,920 | 2,300 |
| 10 | 2,500 | 2,900 | 3,500 | 4,200 |
| 12 | 3,900 | 4,600 | 5,600 | 6,700 |
| 15 | 7,000 | 8,300 | 10,000 | 12,000 |
| Pipe (in) | Horiz. branch | Per interval | Stack ≤ 3 int. | Stack > 3 int. |
|---|---|---|---|---|
| 1½ | 3 | 2 | 4 | 8 |
| 2 | 6 | 6 | 10 | 24 |
| 2½ | 12 | 9 | 20 | 42 |
| 3 | 20 | 20 | 48 | 72 |
| 4 | 160 | 90 | 240 | 500 |
| 5 | 360 | 200 | 540 | 1,100 |
| 6 | 620 | 350 | 960 | 1,900 |
| 8 | 1,400 | 600 | 2,200 | 3,600 |
| 10 | 2,500 | 1,000 | 3,800 | 5,600 |
| 12 | 3,900 | 1,500 | 6,000 | 8,400 |
IPC 2021. A building drain serving a water closet must be at least 3 in. Branch values exclude branches of the building drain. Stacks are sized for the total load and may not be smaller than the largest horizontal branch connected.
UPC drain sizing and Hunter demand table
| Pipe (in) | Horizontal | Vertical |
|---|---|---|
| 1¼ | 1 | 1 |
| 1½ | 1 | 2 |
| 2 | 8 | 16 |
| 3 | 35 | 48 |
| 4 | 216 | 256 |
| 5 | 428 | 600 |
| 6 | 720 | 1,380 |
| 8 | 2,640 | 3,600 |
| 10 | 4,680 | 5,600 |
| 12 | 8,200 | 8,400 |
Excludes trap arms. At 1/8 in/ft, multiply horizontal capacity by 0.8. Water closets may not discharge into 2-in pipe, and 3-in pipe is limited to a small number of water closets (see the footnote in your edition).
| WSFU | Flush tanks | Flushometer valves |
|---|---|---|
| 5 | 9.4 | 15 |
| 10 | 14.6 | 27 |
| 20 | 19.6 | 35 |
| 30 | 23.3 | 42 |
| 50 | 29.1 | 50 |
| 100 | 43.5 | 67.5 |
| 200 | 65 | 90 |
| 300 | 85 | 108 |
| 500 | 124 | 143 |
| 1,000 | 208 | 208 |
Hunter's curve. The flushometer column starts at 5 WSFU; both columns meet at about 1,000 WSFU. UPC projects use the similar curve in UPC Appendix A where adopted.
Worked example and sources
A two-bath house under the IPC (private): 2 bathroom groups (2 × 5 = 10 DFU, 2 × 3.6 = 7.2 WSFU), a kitchen sink (2 DFU, 1.4 WSFU), a dishwasher (2, 1.4), a clothes washer (2, 1.4) and a laundry tray (2, 1.4). Total 18 DFU and 12.8 WSFU. With flush tanks, 12.8 WSFU interpolates to about 16.4 gpm. A building drain carrying a water closet must be at least 3 in, and 3 in carries 42 DFU at 1/4 in/ft, so a 3-in building drain is the minimum.
Summary
This fixture unit calculator totals drainage fixture units (DFU) and water supply fixture units (WSFU) from fixture counts using the model-code tables: IPC 2021 Table 709.1 and Appendix E Table E103.3(2), or UPC 2021 Table 702.1 and Table 610.3, with separate private and public values. It converts the WSFU total to an estimated peak demand with the Hunter curve in IPC Table E103.3(3) and reads minimum drain sizes from IPC Tables 710.1(1) and 710.1(2) or UPC Table 703.2. Local amendments and utility rules vary, so the results are planning values, not sealed designs.
How it works
- Select the model code (IPC or UPC) and the occupancy: private (dwellings, private bathrooms) or public (offices, schools, restaurants and other shared use).
- Enter whole-number counts for each fixture. The DFU and WSFU columns show the values that apply to the selected code and occupancy.
- Click Calculate to total DFU and WSFU. Fixtures that the selected table does not rate are listed separately and excluded rather than guessed.
- Choose whether the water system serves mostly flush tanks or flushometer valves; the WSFU total is converted to peak GPM by interpolating the Hunter demand table.
- Read the minimum building drain, horizontal branch, and stack sizes for the DFU total, then confirm them against the adopted code edition and local amendments.
Use cases
- Preparing a schematic fixture unit schedule for residential or commercial plan review.
- Sizing a building drain or sewer from the total DFU at 1/4 or 1/8 inch per foot slope.
- Estimating peak water demand in GPM for a service line or meter application.
- Comparing IPC and UPC loads for the same fixture program.
- Checking plumbing apprenticeship and licensing exam exercises.