HydroCAD Stormwater Modeling - Since 1986

Units Definitions

English vs. Metric Units

HydroCAD provides complete English and metric (SI) capabilities.  The units used for reports, data entry, and data storage may be independently selected for each project.  This includes the ability to handle mixed units, such as data entry in English with concurrent reports in metric.

Use Settings|Units to change the units for the current project.  This is available on all programs starting with version 6.0.  With this capability, the need for separate English and Metric versions of HydroCAD is eliminated.

Most applications will use the standard English or Metric definitions.  For small sites you may prefer to use the predefined English-LowFlow or Metric-LowFlow options, which add additional decimal places to all of the flow and volume parameters.

By default, all new projects use English units.  If you prefer a different default, such as Metric, you can create a "default" project with the desired settings.  For details, see "Default Settings" in the HydroCAD help index.

Understanding "Large Units"

In addition to the basic English/Metric options described above, each project contains a Large Units option, which lets you choose between two sets of area and volume units, as follows:

Units System=



Large Units= On Off On Off
Areas: Acres Square-Feet Hectares Square-Meters
Volumes: Acre-Feet Cubic-Feet Mega-Liters Cubic-Meters

In addition to the project-wide setting (on the Settings|Units screen), an individual Large Units options is available on each subcatchment and pond.  This is allows each project to contain a wide range of pond or subcatchment sizes, with some nodes described in acres, and others in square feet.  For easy project-wide comparisons, all hydrograph volumes are reported in the same units, as selected on the Settings|Units screen.

Custom Units & Rounding

If you need further control of numeric formatting, rounding, or maximum values, you customize the settings that are used for input and output of each parameter:

For HydroCAD 8.0 and later, click the Custom button on the Settings|Units screen.  This will display a complete set of parameters that can be customized.  Check the box next to the parameter(s) you want to customize and make the desired changes.  Your customization is stored within the individual project file, and will be used by anyone who opens the file.

For HydroCAD 7.1 and earlier, you must create a custom units definition file as described here.  Although this capability is still available in later versions, using the Custom button is generally preferable, as described above.

Warning: Incorrect units settings can cause hard-to-detect errors in data entry or reporting! Before customizing any parameters, make sure you have explored the other options listed above.


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