Total Equivalent Length Calculator
Sum straight duct length and fitting equivalents.
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ⓘ Live results
Results
- Total equivalent length
- 80 ft
- Fitting share of total
- 43.8%
Quick answer
Total equivalent length (TEL) is the straight duct length plus the equivalent lengths of every fitting along the run's longest path.
TEL = straight length + sum of fitting equivalent lengths
How to use the Total Equivalent Length Calculator
- 1Measure the straight duct length along the run's longest path from supply plenum to the farthest register.
- 2Add up the equivalent lengths of every elbow, tee, transition and damper along that path.
- 3Use the total in a friction-rate calculation to size the duct.
Worked example
Using the values the calculator loads with:
Inputs
- Straight duct length45 ft
- Total fitting equivalent length35 ft
Results
- Total equivalent length80 ft
- Fitting share of total43.8%
Frequently asked questions
Which path do I use?
Always the single longest path in equivalent length through the whole system — that path sets the friction rate for the entire design.
Why not just use straight length?
Fittings often add more resistance than the straight runs themselves, especially in tight mechanical rooms.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
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Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.