Sanitary Drain DFU Sizing
Total drainage fixture units from a fixture list and the minimum pipe size for a horizontal branch, vertical stack.
Example
You enter
- Fixtures water closet private 1, lavatory 1, bathtub 1
- Configuration horizontal_branch
- Slope (building drain) 0.25
You get
- Total DFU load 6
- Minimum pipe size 2
Details, formula, and sources
Total drainage fixture units from a fixture list and the minimum pipe size for a horizontal branch, vertical stack, or building drain. Per IPC 2021 §710 with Table 709.1 DFU values.
total DFU = sum(fixture count × DFU value). Minimum pipe size = smallest size whose table maximum ≥ total DFU: horizontal branch and stack per IPC Table 710.1(2); building drain per IPC Table 710.1(1) (slope-dependent).
IPC 2021 (International Plumbing Code). Section 710; DFU values per IPC Table 709.1; capacities per Tables 710.1(1) and 710.1(2).
Free read-only access at codes.iccsafe.org.
Estimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.
Field names used by the API: fixtures, config, slope_in_per_ft, total_dfu, min_size_in
- DFU values IPC Table 709.1 (private WC 3, public WC 4, lavatory 1, bath 2, shower 2, kitchen sink 2, urinal 4, floor drain 2, ...)IPC 2021 Table 709.1
- Branch / stack capacity IPC Table 710.1(2) max DFU by nominal sizeIPC 2021 Table 710.1(2)
- Building-drain capacity IPC Table 710.1(1) max DFU by size and slope (1/8 / 1/4 / 1/2 in per ft)IPC 2021 Table 710.1(1)