Hydroelectric Power Calculator
The power a stream or dam can generate from its head and flow, and what that comes to over a year.
Water falling through a head H at a flow Q carries ρ·g·Q·H watts — 9.
How the hydroelectric power calculator works
Water falling through a head H at a flow Q carries ρ·g·Q·H watts — 9.81 kW for every cubic meter per second falling one meter — and a turbine and generator keep 70–90% of it. A plant rarely runs flat out all year, so annual energy is rated power × hours × capacity factor. The household figure is an input, because an average home’s consumption differs by country.
Formula: P = ρ · g · Q · H · η; annual energy = P × 8,760 h × capacity factor
Worked examples
| Inputs | Rated power | Note |
|---|---|---|
| 25 m head, 2 m³/s, 85% efficient | 417 kW | 417 kW |
| 80 ft head, 70 cfs | 403 kW | 403 kW |
| A micro-hydro creek: 10 m, 0.05 m³/s | 3 kW | 3.4 kW |
FAQFrequently asked questions
What head and flow does a home micro-hydro need?
A few kilowatts needs either a big drop or a lot of water: 10 m of head with 50 L/s gives about 3.5 kW at 70% efficiency. Under 1 kW is still worthwhile because it runs day and night.
What efficiency should I use?
Large turbines reach 90% or more; small Pelton and crossflow units 60–80% including the generator. Friction in the penstock reduces the usable head further — enter net head if you know it.
What is capacity factor?
The share of the year the plant produces its rated output. A run-of-river plant with seasonal flows might average 40–60%, a dam with storage higher. It converts rated kilowatts into a year’s kilowatt-hours.
Why is household consumption an input?
Because it differs several-fold between countries — roughly 2,700 kWh a year in the UK, 5,500 in Australia, 10,500 in the US — so any single baked figure would be wrong for two of the three.
Where these figures come from
- UK DESNZ / DEFRA — Greenhouse gas reporting: conversion factors — the flight, fuel and waste emission factors used here
- Scarborough et al. (2014), Climatic Change — Dietary greenhouse gas emissions — the per-diet daily emission figures
- US EPA — Technical Assistance Document for the Reporting of Daily Air Quality (AQI) — the PM2.5 breakpoints the air quality calculator uses
- US EPA — Greenhouse Gas Equivalencies Calculator — the official US equivalency factors
Last checked: September 2026. Factors are taken from published government and peer-reviewed sources, each named on the page with its year.