Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!


Power potential vs. head and flow rate.

Online Hydro-power Calculator

The calculator below can be used to calculate available hydroelectricity power.

The theoretically power available from falling water can be expressed as

Pth = ρ q g h                      (1)


Pth = power theoretically available (W)

ρ = density (kg/m3) (~ 1000 kg/m3 for water)

q = water flow (m3/s)

g = acceleration of gravity (9.81 m/s2)

h = falling height, head (m)

hydropower, volume flow, head and power generation

Download and print Hydro Power vs. Volume Flow and Head chart

Example - Hydro-power

The theoretically power available from a flow of 1 m3/s water with a fall of 100 m can be calculated as

P = (1000 kg/m3) (1 m3/s) (9.81 m/s2) (100 m)

  = 981 000 W

  = 981 kW


Due to energy loss the practically available power will be less than the theoretically power. Practically available power can be expressed as

Pa = μ ρ q g h                (2)


Pa = power available (W)

μ = efficiency (in general in the range 0.75 to 0.95)

Energy from Hydro-power

The potential theoretical energy in a volume of elevated water can be calculated

W = m g h

     = ρ V g h                      (3)


W = energy (J)

m = mass of water (kg)

V = volume of water (m3)

Example - Energy in Elevated Water Volume

10 m3 volume of water is elevated 10 m above the turbine. The potential energy in the water volume can be calculated as

W = (1000 kg/m3) (10 m3) (9.81 m/s2) (10 m)

   = 981000 J (Ws)

   = 981 kJ (kWs)

   = 0.27 kWh

Potential Energy in a Tank or Reservoir

Energy water reservoir

You can estimate the total energy in a tank or a reservoir where the surface area varies with elevation - as typical in a natural reservoir - by integrating the potential energies for horizontal segments as done in the template

Potential energy accumulated in a water reservoir - hydro power

Copy the document to your Google Drive or download it as a spreadsheet to make your own calculations. 

Related Topics

  • Environment

    Climate, meteorology, solar, wind, emissions and environmental related engineering resources.

Related Documents


Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .


This page can be cited as

  • The Engineering ToolBox (2008). Hydropower. [online] Available at: [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter