Total Equivalent Length Calculator
Sum straight duct length and fitting equivalents.
Enter your values
Enter the straight duct length in ft.
Enter the total fitting equivalent length in ft.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
At a glance
| What it does | Sum straight duct length and fitting equivalents. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Straight duct length, Total fitting equivalent length |
| Main output | Total equivalent length |
| Formula | TEL = straight length + sum of fitting equivalent lengths |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Straight duct length(ft)
- Enter the straight duct length in ft.
- Total fitting equivalent length(ft)
- Enter the total fitting equivalent length in ft.
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.
What do I need to enter into the Total Equivalent Length Calculator?
Just 2 values: straight duct length, total fitting equivalent length. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Total Equivalent Length Calculator work out the answer?
Total equivalent length (TEL) is the straight duct length plus the equivalent lengths of every fitting along the run's longest path. It applies the formula TEL = straight length + sum of fitting equivalent lengths and shows the working so you can check each step by hand.
Is the Total Equivalent Length Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.