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 3
Checked against published worked examples from: ICC.
Details, formula, and sources
ScopeTotal drainage fixture units from a fixture list and the minimum pipe size for a horizontal branch, vertical stack, or building drain. Per IPC 2027 §710 with Table 709.1 DFU values (unchanged from 2021 except the drinking fountain, now 0 DFU).
Formula or tabletotal 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).
Source and editionIPC 2027 (International Plumbing Code). Section 710; DFU values per IPC Table 709.1; capacities per Tables 710.1(1) and 710.1(2).
Free accessFree read-only access at codes.iccsafe.org.
What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.
API field namesfixtures, 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 2027 Table 709.1 (identical in 2021 except the drinking fountain, 1/2 DFU then, 0 now)
- Branch / stack capacity IPC Table 710.1(2) max DFU by nominal sizeIPC 2027 Table 710.1(2) (identical in 2021)
- Building-drain capacity IPC Table 710.1(1) max DFU by size and slope (1/8 / 1/4 / 1/2 in per ft)IPC 2027 Table 710.1(1) (identical in 2021)