Duct Calculator - HVAC, Duct Sizing Software

            Duct Calculator - HVAC Duct Sizing
                                 Software Ver 1.0.1

The purpose of creating this type of program is to reduce the overall time spent designing duct systems. The result is a reduction in time required to look up the duct sizing information from duct charts, devices and books. The software is reasonably accessible from the desktop or laptop computer at the designer's and engineer's fingertips. Therefore, the expenditure for the software has a payback of less than one hour of an engineer's billing time.

Setting the Highest Standard

Duct Calculator sets the highest standard in the world of duct sizing or evaluating of pre-sized ducts calculator programs. By giving you the ability to perform residential, commercial and industrial HVAC duct sizing, it gives you something no other program of its kind can. Download the demonstration version today and see why Duct Calculator is unparalleled in its field.


  • English or SI Metric Units to choose from.
  • Sizing and evaluating of round, rectangular and oval ducts, all calculated at the same time.
  • The methodology for determining the duct friction loss is the Darcy-Weisbach formula, as demonstrated in the ASHRAE Handbook of Fundamentals.
  •  Air flow, density, viscosity, velocity, Reynolds number, friction factor, relative roughness, roughness factor, friction loss, duct nominal diameter, rectangular and oval sizes of the duct can be reviewed or printed at the user's option.
  • Friction loss per 100 feet of duct from 0.01 in w.g.(0.08 Pa/m) to 4 in w.g.(32.7 Pa/m).
  • Maximum air velocity from 0 fpm, (0 m/s) to 12,000 fpm (60.9 m/s) to choose from.
  • Fluid properties density and viscosity are calculated automatically.
  • Air temperature from 35 oF (1.7 oC) to 250 oF (121.2oC) to choose from.
  • Elevations from 0 feet (0 m) to 10,000 feet (3,048m).
  • Thirteen types of duct materials, roughness categories and absolute roughness (e, ft) to choose from.
  • Quick lookup of type of duct materials and maximum air velocity recommendations at the user's fingertips.
  • Input error checking


Duct Calculator is a program that computes optimal duct sizes for HVAC duct systems in residential, commercial and industrial buildings. Duct Calculator size ducts and evaluates ducts sizes with the Darcy-Weisbach equation as recommended by ASHRAE Handbook of Fundamentals.


The equation used for sizing ducts is the Darcy-Weisbach. The program determines duct sizes from 2-inches (5.08 cm) to 100-inches (254 cm) for round, rectangular and oval ducts.

All the information you enter into Duct Calculator, is checked for correctness, and the calculated results are returned so Duct Calculator can create formatted, useful output.

The equation’s allows the program to obtain exactly the same results that you would obtain manually.

Therefore, the output can be quickly and easily verified by hand so that you can have the utmost confidence an assurance in the program output.

Program Input

Duct Calculator Is a true Windows program complete with toolbars and hyperlinked help file and PDF Manual. All data is checked during the calculation period.

The type of information required for computations are the elevation, feet (m), air temperature deg F (deg C), type of duct material, maximum velocity, fpm (m/s) and height of the duct constraints, inches (cm), desired maximum duct loss per 100 feet of duct, in w.g.(Pa/m) and the air flow through the duct in cubic feet minute, cfm (m3/s).

Program Output

Duct Calculator, provides a detailed report of the duct computations for review or printing. The information contained in the report is the air flow rate, cfm (m3/s), Velocity, fps (m/s), Density, lb/cuft (kg/m3), Viscosity, CentiPosies (cP), Reynolds Number, Friction Factor, Relative Roughness (e, ft), Roughness Factor (e/D), Nominal Duct Diameter, inches (cm), Friction loss of the duct per 100 feet duct, in w.g. (Pa/m).

One Version Available

Duct Calculator can be purchased in one form: The program costs $95.00.

Screen Snap Shots


 Menu Bar

Main Window

Pre-Size Window

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