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Physics · Grades 8–11

Energy in kilowatt-hours

A kilowatt-hour is energy, not power.

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Rule and assumptions

A kilowatt-hour is energy, not power.

E(kWh) = P(W) × t(h)/1000

Worked examples

A model device uses constant power 1800 W for 6 h. Find the energy in kilowatt-hours. Round to 3 decimal places if needed. Answer in kWh.

E(kWh) = P(W) × t(h)/1000 1800 × 6 / 1000 = 10.8

10.8 kWh

A model device uses constant power 50 W for 12 h. Find the energy in kilowatt-hours. Round to 3 decimal places if needed. Answer in kWh.

E(kWh) = P(W) × t(h)/1000 50 × 12 / 1000 = 0.6

0.6 kWh

Try two questions

  1. A model device uses constant power 725 W for 20 h. Find the energy in kilowatt-hours. Round to 3 decimal places if needed. Answer in kWh.

  2. A model device uses constant power 1500 W for 20 h. Find the energy in kilowatt-hours. Round to 3 decimal places if needed. Answer in kWh.

Answers and reasoning

Answers and marking notes
  1. 14.5 kWh

    E(kWh) = P(W) × t(h)/1000 725 × 20 / 1000 = 14.5

  2. 30 kWh

    E(kWh) = P(W) × t(h)/1000 1500 × 20 / 1000 = 30

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Learning preview · independent educational and translation review required. Suggested grades are not official curriculum alignment.