Building Code Glossary
Equivalent Length: Building Code Definition
How the IRC 2009 define equivalent length, where the wording differs, and which chapters depend on the term.
On this page
Last updated September 7, 2026 · Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.
Direct answer
Equivalent length is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “For determining friction losses in a piping system, the effect of a particular fitting equal to the friction loss through a straight piping length of the same nominal diameter.” No other I-Code in this corpus defines it, so the IRC 2009 definition is the one to work from. The term is used in 5 chapters of this corpus, most often in Exhaust Systems (IMC 2009), Fuel Gas (IRC 2009), Exhaust Systems (IRC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted. Record the jurisdiction, the adopted edition, the application date and any local amendment that rewrites the definition before you use it on a live project, because a term redefined by amendment changes every requirement that depends on it.
Content and cited inputs reviewed by Scott Barrington, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Equivalent Length — IRC 2009, Definitions:
For determining friction losses in a piping system, the effect of a particular fitting equal to the friction loss through a straight piping length of the same nominal diameter.
What must be verified before using this guidance?
Equivalent Length is defined once in this corpus, in the Definitions chapter of the International Residential Code (IRC) 2009:
For determining friction losses in a piping system, the effect of a particular fitting equal to the friction loss through a straight piping length of the same nominal diameter.
Where equivalent length is used in the code
The term appears in 5 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Exhaust Systems | IMC 2009 | 7 |
| Fuel Gas | IRC 2009 | 7 |
| Exhaust Systems | IRC 2009 | 5 |
| Definitions | IRC 2009 | 1 |
| Water Supply and Distribution | IRC 2009 | 1 |
The term in use
How the code actually writes about equivalent length, quoted from the 2009 text hosted here:
In the absence of fitting equivalent length calculations from the clothes dryer manufacturer, Table 504.6.4.1 shall be used.
In the absence of fitting equivalent length calculations from the clothes dryer manufacturer, Table G2439.5.5.1 shall be used.
In the absence of fitting equivalent length calculations from the clothes dryer manufacturer, Table M1502.4.4.1 shall be used.
The size of water service mains, branch mains and risers shall be determined according to water supply demand [gpm (Lim)], available water pressure [psi (kPa)] and friction loss caused by the water meter and developed length of pipe [feet (m)], including equivalent length of fittings.
The terms equivalent length is built out of
The definition above leans on 5 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what equivalent length covers:
- Piping System — IRC 2009: All fuel piping, valves and fittings from the outlet of the point ofdeliveryto the outlets of the appliance shutoff valves.
- Diameter — IRC 2009: Unless specifically stated, the term "diameter" is the nominal diameter as designated by the approved material standard.
- Fitting — IRC 2009: An accessory such as a locknut, bushing or other part of a wiring system that is intended primarily to perform a mechanical rather than an electrical function.
- Piping — IRC 2009: Where used in this code, “piping” refers to either pipe or tubing, or both.
- System — IFC 2009: An assembly of equipment consisting of a tank, container or containers, appurtenances, pumps, compressors and connecting piping.
Equivalent Length: what to open, and in what order
Every row is a document this term depends on. The ICC code library and the ICC adoption maps cover the middle rows.
| Check | Where | Confirmed |
|---|---|---|
| Read the definition in the adopted IRC | Definitions | |
| Re-check the requirement that uses it | Exhaust Systems (IMC 2009) | |
| Re-check the requirement that uses it | Fuel Gas (IRC 2009) | |
| Re-check the requirement that uses it | Exhaust Systems (IRC 2009) | |
| Re-check the requirement that uses it | Definitions (IRC 2009) | |
| Confirm the dependent definition | Piping System | |
| Confirm the dependent definition | Diameter | |
| Confirm the dependent definition | Fitting | |
| Local amendment to any of the above | Jurisdiction's amendment list |
A research aid, not a code determination. The authority having jurisdiction decides which edition and which amendments apply.
Where can you explore related guidance?
- Explore all glossary guidance
- Piping System: Building Code Definition
- Diameter: Building Code Definition
- Fitting: Building Code Definition
- System: Building Code Definition
Sources and method
Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The ICC code library publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.
Source links
Frequently asked questions
What is the code definition of equivalent length?
The International Residential Code (IRC) 2009 defines it in Definitions as: “For determining friction losses in a piping system, the effect of a particular fitting equal to the friction loss through a straight piping length of the same nominal diameter.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.
Which parts of the code depend on equivalent length?
In this corpus the term is used across 5 chapters, led by Exhaust Systems in the IMC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.
What does equivalent length mean?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “For determining friction losses in a piping system, the effect of a particular fitting equal to the friction loss through a straight piping length of the same nominal diameter.” It is defined in IRC 2009. Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.
What is the equivalent length of a 90 degree elbow?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “For determining friction losses in a piping system, the effect of a particular fitting equal to the friction loss through a straight piping length of the same nominal diameter.” It is defined in IRC 2009. It is not the same as Elbow, which the IRC 2009 defines separately as “A pressure pipe fitting designed to provide an exact change in direction of a pipe run. An elbow provides a sharp turn in the flow path (see "Bend" and "Sweep").” Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.
What does the equivalent length of a duct fitting mean?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “For determining friction losses in a piping system, the effect of a particular fitting equal to the friction loss through a straight piping length of the same nominal diameter.” It is defined in IRC 2009. It is not the same as Fitting, which the IRC 2009 defines separately as “An accessory such as a locknut, bushing or other part of a wiring system that is intended primarily to perform a mechanical rather than an electrical function.” Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.
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