Fixture Units to Pipe Size Reference Values
Lookup practical drainage pipe size by fixture-unit load for horizontal branches and building drains.
On this page
Reference Value Index
This page lists 12 reference values for quick browsing and lookup.
All Reference Values
- Horizontal Branch ≤ 3 DFU = 1-1/2 in
- Horizontal Branch ≤ 8 DFU = 2 in
- Horizontal Branch ≤ 24 DFU = 3 in
- Horizontal Branch ≤ 50 DFU = 4 in
- Horizontal Branch ≤ 180 DFU = 6 in
- Horizontal Branch ≤ 390 DFU = 8 in
- Building Drain ≤ 2 DFU = 1-1/2 in
- Building Drain ≤ 6 DFU = 2 in
- Building Drain ≤ 20 DFU = 3 in
- Building Drain ≤ 160 DFU = 4 in
- Building Drain ≤ 360 DFU = 6 in
- Building Drain ≤ 700 DFU = 8 in
Reference Table
| System | Max DFU | Pipe Size | Min Slope (in/ft) |
|---|---|---|---|
| Horizontal Branch | 3 | 1-1/2 in | 0.25 |
| Horizontal Branch | 8 | 2 in | 0.25 |
| Horizontal Branch | 24 | 3 in | 0.125 |
| Horizontal Branch | 50 | 4 in | 0.125 |
| Horizontal Branch | 180 | 6 in | 0.125 |
| Horizontal Branch | 390 | 8 in | 0.125 |
| Building Drain | 2 | 1-1/2 in | 0.25 |
| Building Drain | 6 | 2 in | 0.25 |
| Building Drain | 20 | 3 in | 0.125 |
| Building Drain | 160 | 4 in | 0.125 |
| Building Drain | 360 | 6 in | 0.125 |
| Building Drain | 700 | 8 in | 0.125 |
Frequently Asked Questions
Frequently asked questions for Fixture Units to Pipe Size and its reference values.
What are drainage fixture units (DFU)?
DFU is a plumbing design unit that represents probable drainage load from fixtures and helps size drainage piping.
Why are branch and building drain tables different?
Different parts of the drainage system can have different loading and sizing rules, so lookup limits vary by system type.
Does this replace full plumbing code tables?
No. Use this as a quick planning reference; final design must follow adopted local plumbing code and authority requirements.
Why include minimum slope with pipe size?
Adequate slope is essential for gravity drainage performance and is typically tied to pipe size and code requirements.
Methodology and Review
Each row on this page links to a value detail page derived from the same conversion data file as the main calculator and reference table. This reduces inconsistencies across page variants.
Editorial metadata and structured data are rendered across the converter page and linked value pages. Review policies are documented in our review process and editorial policy.