Utility Demand Per Capita Calculator
The demand a population places on a utility — average and peak — from a per-capita rate and a peaking factor, for water, sewerage, power or gas.
Average demand is population times a per-capita rate.
How the utility demand per capita calculator works
Average demand is population times a per-capita rate. Infrastructure is not sized for the average, though: it is sized for the peak, which is the average times a peaking factor of 1.5 to 3 depending on the utility and the size of the area.
Small areas peak harder than large ones, because there is less averaging across households. That is why a trunk main is sized differently from a street main serving fifty houses.
Formula: average = population × rate; peak = average × peaking factor
Worked examples
| Inputs | Average daily demand | Note |
|---|---|---|
| 12,000 people at 180 L | 2.16 ML | 2.16 ML a day, 4.75 at peak |
| Electricity | 96 MWh | 96 MWh a day |
| A small subdivision | 72 kL | peaks harder |
FAQFrequently asked questions
What is a peaking factor?
The ratio of peak demand to average. Water mains use 2 to 3 for the peak day; electricity networks 1.5 to 2; the smaller the area, the higher the factor.
How much water does a person use?
Between 150 and 250 litres a day in most developed cities, including garden and outdoor use. Indoor-only is 100 to 140.
Why size for peak rather than average?
Because a main that meets the average fails on the hottest day of the year, which is exactly when it matters.
What growth should I design for?
The planning horizon of the asset — 25 to 50 years for pipes. Under-sizing a trunk main is far more expensive to fix than over-sizing it.
Does this cover sewerage?
Yes — use the water rate less garden use, typically 70 to 80% of it, with a peaking factor for wet-weather inflow.
Where these figures come from
- UN-Habitat — Urban Indicators Guidelines — density, green space and public space benchmarks
- World Health Organization — Urban green spaces — the 9 m² per person minimum
- ITE — Parking Generation Manual — parking demand rates by land use
- Office for National Statistics — Population estimates — the UK's national statistics agency
Last checked: September 2026. Default per-capita rates are mid-range figures from national statistical agencies and utility reports; every one is an input you should replace with the local figure.