Cost Per Watt Hour Calculator
Find the cost of a single Watt-hour (Wh) of energy based on the total energy cost and the total energy consumed in Watt-hours.
Enter the total amount paid for energy and the total energy consumed for that cost.
Enter Energy Cost and Usage
Understanding Energy Cost Per Watt Hour
What is Cost Per Watt Hour (Wh)?
Cost Per Watt Hour is a unit rate representing how much you pay for one Watt-hour of electrical energy. While utility bills typically state usage in kilowatt-hours (kWh), breaking it down to Watt-hours gives you a very granular cost figure, useful for analyzing the cost effectiveness of small devices or specific periods of low usage.
The Calculation
The calculation is straightforward:
Cost Per Wh = Total Cost / Total Watt-Hours
It assumes the Total Cost provided corresponds exactly to the Total Watt-Hours consumed. For a typical energy bill, this calculates your *average* cost per Wh over that billing period, taking into account different rate tiers or usage-based fees included in the Total Cost.
Converting kWh to Wh
Your energy bill will most likely show usage in kilowatt-hours (kWh). To convert kWh to Watt-hours (Wh), remember that 1 kWh = 1000 Wh.
Total Watt-Hours (Wh) = Total Kilowatt-Hours (kWh) * 1000
So, if your bill says you used 50 kWh, your total Watt-hours is 50 * 1000 = 50,000 Wh.
Cost Per Watt Hour Examples
Here are 10 examples demonstrating how to use the calculator with different inputs:
Example 1: Simple Calculation
Scenario: Your energy bill for a month is $50.00, and you used 250 kWh.
1. Convert kWh to Wh: 250 kWh * 1000 = 250,000 Wh.
2. Enter Values: Total Cost = 50.00, Total Watt-Hours = 250000.
3. Calculate: Cost Per Wh = $50.00 / 250,000 Wh.
4. Result: $0.0002 per Wh.
Example 2: Higher Rate
Scenario: You used 100 kWh and the cost was $20.00.
1. Convert kWh to Wh: 100 kWh * 1000 = 100,000 Wh.
2. Enter Values: Total Cost = 20.00, Total Watt-Hours = 100000.
3. Calculate: Cost Per Wh = $20.00 / 100,000 Wh.
4. Result: $0.0002 per Wh.
Example 3: Lower Usage, Same Rate
Scenario: You used 50 kWh and the cost was $10.00.
1. Convert kWh to Wh: 50 kWh * 1000 = 50,000 Wh.
2. Enter Values: Total Cost = 10.00, Total Watt-Hours = 50000.
3. Calculate: Cost Per Wh = $10.00 / 50,000 Wh.
4. Result: $0.0002 per Wh.
Example 4: Different Currency
Scenario: Your bill was €75.00 for 300 kWh.
1. Convert kWh to Wh: 300 kWh * 1000 = 300,000 Wh.
2. Enter Values: Total Cost = 75.00, Total Watt-Hours = 300000.
3. Calculate: Cost Per Wh = €75.00 / 300,000 Wh.
4. Result: €0.00025 per Wh.
Example 5: Small Usage Cost
Scenario: You want to know the cost per Wh if $0.75 was spent on 3000 Wh.
1. Enter Values: Total Cost = 0.75, Total Watt-Hours = 3000.
2. Calculate: Cost Per Wh = $0.75 / 3000 Wh.
3. Result: $0.00025 per Wh.
Example 6: High Usage Scenario
Scenario: A large facility uses 5000 kWh in a month costing $900.
1. Convert kWh to Wh: 5000 kWh * 1000 = 5,000,000 Wh.
2. Enter Values: Total Cost = 900.00, Total Watt-Hours = 5000000.
3. Calculate: Cost Per Wh = $900.00 / 5,000,000 Wh.
4. Result: $0.00018 per Wh.
Example 7: Low Cost, Low Usage
Scenario: You spent $0.25 on 1000 Wh (1 kWh).
1. Enter Values: Total Cost = 0.25, Total Watt-Hours = 1000.
2. Calculate: Cost Per Wh = $0.25 / 1000 Wh.
3. Result: $0.00025 per Wh.
Example 8: Using Pence and Wh
Scenario: The energy used cost 6000 pence for 20,000 Wh.
1. Enter Values: Total Cost = 6000 (pence), Total Watt-Hours = 20000.
2. Calculate: Cost Per Wh = 6000 pence / 20,000 Wh.
3. Result: 0.3 pence per Wh (or £0.003 per Wh if calculating in pounds).
Example 9: High Decimals
Scenario: A small energy amount, 500 Wh, costs $0.12.
1. Enter Values: Total Cost = 0.12, Total Watt-Hours = 500.
2. Calculate: Cost Per Wh = $0.12 / 500 Wh.
3. Result: $0.00024 per Wh.
Example 10: Comparing Costs
Scenario: Bill A is $80 for 400 kWh. Bill B is $100 for 450 kWh. Compare cost per Wh.
Bill A: 400 kWh = 400,000 Wh. $80 / 400,000 Wh = $0.0002 per Wh.
Bill B: 450 kWh = 450,000 Wh. $100 / 450,000 Wh ≈ $0.000222 per Wh.
1. Enter Values (Bill A): Cost = 80, Wh = 400000. Result: $0.0002 per Wh.
2. Enter Values (Bill B): Cost = 100, Wh = 450000. Result: $0.000222 per Wh.
Conclusion: Bill A had a slightly lower average cost per Wh.
Frequently Asked Questions about Cost Per Watt Hour
1. What is a Watt-Hour (Wh)?
A Watt-hour (Wh) is a unit of energy equivalent to consuming one watt of power for one hour. It's a very small unit compared to the kilowatt-hour (kWh) typically used on energy bills.
2. How is Cost Per Wh different from Cost Per kWh?
Cost Per kWh is the price you pay for one kilowatt-hour, while Cost Per Wh is the price you pay for one Watt-hour. Since 1 kWh = 1000 Wh, the Cost Per Wh will be 1/1000th of the Cost Per kWh (or Cost Per kWh = Cost Per Wh * 1000).
3. Why would I calculate Cost Per Wh instead of just Cost Per kWh?
Calculating Cost Per Wh gives you a very precise unit cost, which can be useful for academic purposes, specific detailed energy consumption analysis, or comparing very small energy usage amounts.
4. How do I get the "Total Cost" and "Total Watt-Hours"?
These typically come from your energy bill. The bill will state the total amount due (your "Total Cost") and the total energy consumed, usually in kWh. You'll need to convert the total kWh to Wh by multiplying by 1000.
5. Does the calculated Cost Per Wh include taxes and fees?
If you use the total amount from your energy bill as the "Total Cost," then the resulting Cost Per Wh is an *average* unit cost that implicitly includes all usage-based charges, taxes, and fees that are part of that total bill amount. It wouldn't include fixed monthly service fees unrelated to consumption.
6. Can I use this for any currency?
Yes, you can use any currency for the "Total Cost." The result will be in that same currency per Watt-hour.
7. What if my energy usage is zero?
If your "Total Watt-Hours" is zero, the calculator will show an error because you cannot divide by zero. Energy cost is only applicable when energy is consumed.
8. What if the cost is zero but usage is positive?
If the "Total Cost" is zero and "Total Watt-Hours" is positive, the result will be 0 per Wh. This might occur if you had a credit, a special promotional period, or a billing adjustment.
9. Is this calculation applicable to all types of energy (electricity, gas)?
This calculator specifically uses "Watt-Hours," which is a unit for electrical energy. While gas bills also have a total cost and usage, gas usage is typically measured in therms or cubic meters/feet, not Watt-hours. You would need a different calculator for gas.
10. How accurate is the calculated Cost Per Wh?
The accuracy depends entirely on the accuracy of your input values (Total Cost and Total Watt-Hours). If you use the exact numbers from your bill, it accurately calculates your *average* cost per Wh for that specific billing period.
