Electricity Cost Calculator: Cost of Running an Appliance

What it costs to run an appliance.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose which quantity you want to find.

Enter the other values in the units shown.

The calculator gives the answer with the formula, the substituted numbers, and the answer in other units.

Formulas used

  • C = P\,t\,r
  • r = \frac{C}{P\,t}

Worked example

With the default numbers in the calculator above:

  1. The formula, arranged to find the cost: cost = power of the appliance x time it runs x price of electricity
  2. Put the values in (every value in its SI unit): cost = 2 x 3 x 0.3
  3. The answer: cost: 1.8 dollars
  4. The same answer in other units: 54 per 30 days if this is a daily cost; 657 per 365 days if this is a daily cost

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: What do you want to find? Price of electricity; Cost (leave it as it is if this is what you are finding) 1.8 dollars; Power of the appliance (leave it as it is if this is what you are finding) 2 kW; Time it runs (leave it as it is if this is what you are finding) 3 hours.

  1. The formula, arranged to find the price of electricity: price of electricity = (cost) / (power of the appliance x time it runs)
  2. Put the values in (every value in its SI unit): price of electricity = (1.8) / (2 x 3)
  3. The answer: price of electricity: 0.3 dollars per kWh
  4. The same answer in other units: 30 cents per kWh

Common questions

How do I work out what an appliance costs to run?

Multiply the power in kilowatts by the hours used and by the price per kWh. A 2 kW heater for 3 hours at 30 cents is 1.80 dollars.

How do I convert watts to kilowatts?

Divide by 1000.

What is a kilowatt hour?

The energy used by a 1 kW appliance running for 1 hour, which is 3.6 million joules.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any school physics text (electrical energy and cost).

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