Elbow Equivalent Length Calculator
Equivalent duct length added by fittings.
Enter your values
ⓘ Live results
Results
- Equivalent length per fitting
- 2 ft
- Total equivalent length added
- 6 ft
- Fitting count
- 3
Quick answer
Each duct fitting adds friction equal to a certain length of straight duct, commonly 15-45 equivalent feet per elbow depending on its radius and duct diameter.
Total equivalent length = straight length + sum(fitting equivalent lengths)
How to use the Elbow Equivalent Length Calculator
- 1Enter the duct diameter and the type of fitting used.
- 2Enter how many of that fitting are in the run.
- 3Add the resulting equivalent length to the straight duct length for a total equivalent length.
Worked example
Using the values the calculator loads with:
Inputs
- Duct diameter8 in
- Elbow typeStandard 90° elbow
- Number of fittings3
Results
- Equivalent length per fitting2 ft
- Total equivalent length added6 ft
- Fitting count3
Frequently asked questions
Why do fittings matter so much?
A single poorly chosen branch tee can add as much friction as 15-20 feet of straight duct.
Should I favor long-radius elbows?
Yes where space allows — they roughly halve the equivalent length penalty of a standard short-radius elbow.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.