Fixture Units to Pipe Size
Lookup practical drainage pipe size by fixture-unit load for horizontal branches and building drains.
Building Drain ≤ 2 DFU =
1-1/2 in
Representative value from the Fixture Units to Pipe Size reference table.
Reference Values
Browse 12 reference values with individual detail pages for quick lookup.
Fixture Units to Pipe Size Lookup
Select system type and fixture-unit load to estimate minimum drainage pipe size.
Recommended Pipe Size
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Reference Table
Use this complete table for quick lookup and internal linking to specific value pages.
| 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
Common questions about Fixture Units to Pipe Size, formulas, and typical use cases.
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
This page combines a live calculator, precomputed reference values, and FAQ content from the same conversion definition to reduce mismatch between calculator output and lookup tables.
Editorial metadata (author, reviewer, and update date) is rendered on the page and in structured data. See our editorial policy, review process, and corrections policy.
For compliance-sensitive work, verify final values against project requirements, governing standards, and manufacturer documentation.