25 kWh in a 15-minute interval
25 kWh ÷ 0.25 h = 100 kW. If this is the highest 15-minute interval in the month, 100 kW is the actual peak demand.
Demand, average over the interval 100 kW Open in the calculator
Interval demand calculator
Turn the energy recorded in one demand interval into the average kW over that interval, as a utility calculates demand.
Demand, average over the interval
104kW
Check the values to see a result.
This is the billing peak only if it is the highest interval in the billing period.
How it’s calculated
- P = E ÷ t=52 ÷ 0.5 h=104 kW
P = E × k ÷ (t ÷ 60)
52 kWh in 30 minutes is an average demand of 104 kW over the interval.
Tip: Billing demand is usually the highest interval in the month, so run this on the peak interval, not a typical one.
How to convert kWh per interval to kW
Demand is the average rate of energy use over a fixed interval, usually 15 or 30 minutes. To get it, divide the kWh recorded in the interval by the interval length in hours. 25 kWh in 15 minutes is 25 ÷ 0.25 = 100 kW. The highest interval in the billing period is the peak that a demand charge is based on.
Demand from interval energy
P = E ÷ (t ÷ 60)
E is the kWh in one interval and t its length in minutes. For a 15-minute interval, multiply by 4; for 30 minutes, by 2.
With a meter multiplier
P = E × k ÷ (t ÷ 60)
Where a meter records secondary values from CTs or VTs, k is the combined ratio: 80 for a 400/5 CT. Most modern meters apply it themselves; check the register before multiplying again.
Interval demand is an average, so it is lower than the instantaneous peak. A 200 kW spike lasting one minute adds only about 13 kW to a 15-minute interval, which is why short starts rarely set the billing peak and sustained loads do.
Interval demand examples
A half-hourly reading
Many utilities and settlement systems work in half-hours. 210 kWh in 30 minutes is an average of 420 kW over that half-hour.
Demand, average over the interval 420 kW Open in the calculator
A register that reads through a 400/5 CT
An older meter records 0.3125 kWh on the secondary side of 400/5 CTs. Multiplied by 80 that is 25 kWh on the primary side, and over 15 minutes an average of 100 kW.
Demand, average over the interval 100 kW Open in the calculator
kWh per interval to kW
Average demand for energy recorded in one 15, 30 or 60-minute interval.
| Energy in the interval (kWh) | 15 minutes (kW) | 30 minutes (kW) | 60 minutes (kW) |
|---|---|---|---|
| 1 | 4 | 2 | 1 |
| 2.5 | 10 | 5 | 2.5 |
| 5 | 20 | 10 | 5 |
| 10 | 40 | 20 | 10 |
| 25 | 100 | 50 | 25 |
| 50 | 200 | 100 | 50 |
| 100 | 400 | 200 | 100 |
| 250 | 1,000 | 500 | 250 |
| 500 | 2,000 | 1,000 | 500 |
| 1,000 | 4,000 | 2,000 | 1,000 |
Questions about interval demand
What is the difference between kW and kWh?
kW is a rate, kWh an amount. A 100 kW load running for 15 minutes uses 25 kWh. Interval demand turns the amount in an interval back into the average rate.
Is interval demand the same as billing demand?
Not always. Billing demand may be the highest interval in the month, the highest within certain hours, a ratchet on earlier months, or measured in kVA. The tariff defines it.
Why does my meter show a higher peak than the bill?
A meter or logger reading instantaneous power, or a shorter interval, catches peaks that a 15 or 30-minute average smooths out. Compare figures measured over the same interval.
Limits of this result
- The input must be energy accumulated during one complete fixed demand interval, not a cumulative meter register reading.
- Actual interval demand can differ from billing demand because tariffs may apply ratchets, time windows, coincident-demand rules, power-factor adjustments or minimums.
- Confirm the interval boundary, missing-data treatment and current meter multiplier before comparing results.
Measure it continuously
A ZEM measures demand directly on a circuit. For an existing meter with a pulse output, a ZPC counts the pulses, which give the energy in each interval.
