Hydraulic Diameter Calculator — Rectangular Duct
Hydraulic diameter of a rectangular duct for Re and friction calculations.
Use D_h for Reynolds number, but ASHRAE's D_e (Huebscher) for matching a rectangular duct to round-duct friction charts — they differ.
Formula
Hydraulic Diameter Calculator — Rectangular Duct is a free hydraulic diameter for process, mechanical and water engineers — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Hydraulic Diameter Calculator — Rectangular Duct
Hydraulic diameter of a rectangular duct for Re and friction calculations. The calculation implements D_h = 2ab/(a+b); D_e = 1.30·(ab)^0.625/(a+b)^0.25 (ASHRAE Handbook — Fundamentals, ch. 21). Use D_h for Reynolds number, but ASHRAE's D_e (Huebscher) for matching a rectangular duct to round-duct friction charts — they differ.
How to use Hydraulic Diameter Calculator — Rectangular Duct
- 1Enter Duct width in mm.
- 2Enter Duct height in mm.
- 3Read Hydraulic diameter, Equal-friction equivalent Ø instantly — no submit button needed.
- 4Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Hydraulic Diameter Calculator — Rectangular Duct?
- ✓Implements the standard formula — D_h = 2ab/(a+b); D_e = 1.30·(ab)^0.625/(a+b)^0.25
- ✓Reference cited on-page: ASHRAE Handbook — Fundamentals, ch. 21
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Live worked example: the substitution recomputes from your numbers
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Hydraulic Diameter Calculator — Rectangular Duct use?+
It computes D_h = 2ab/(a+b); D_e = 1.30·(ab)^0.625/(a+b)^0.25, per ASHRAE Handbook — Fundamentals, ch. 21. The formula is displayed under the result along with a worked example substituted with your own inputs.
What should I keep in mind when using this calculator?+
Use D_h for Reynolds number, but ASHRAE's D_e (Huebscher) for matching a rectangular duct to round-duct friction charts — they differ.
Does this work for any fluid?+
Yes — density and viscosity are inputs (with common fluids suggested in the field hints), so the same physics applies to water, oils, gases and process fluids. Compute always runs in SI internally, so unit mix-ups can't corrupt the result.
Is the Hydraulic Diameter Calculator — Rectangular Duct free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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