Power Converter: Tips & How-Tos

Best Practices

Mechanical HP and metric HP (PS) are not identical. 1 mechanical horsepower (hp) = 745.7 W; 1 metric horsepower (PS) = 735.5 W. The difference is about 1.4%. For precise engineering comparisons, always convert to watts.
kW is the SI unit — use it for precise comparisons. Electric vehicles, industrial motors, and international specifications increasingly use kilowatts. When comparing engines from different countries, convert all values to kW to eliminate unit confusion.
Compare continuous rating, not peak. Motors and generators have both a continuous (or rated) power output and a short-term peak. Only compare the same type: a continuous-rated 5 kW motor versus a peak-rated 5 kW generator is not a fair comparison.
BTU/hr is used for HVAC, not engines. Air conditioners and heating systems are rated in BTU per hour, not watts. For HVAC comparisons, use BTU/hr; for engines and motors, use kW or hp.

Watts = Volts × Amps (for resistive loads). For simple resistive loads (heaters, incandescent lights), power in watts equals voltage times current. For motors and reactive loads, the relationship is more complex (power factor applies).
Know your appliance wattage before sizing a generator. Add up the wattage of everything you plan to run simultaneously to determine the generator size you need. Leave at least 20% headroom above the total to allow for startup surges.
Motors draw more power on startup than when running. Electric motors typically draw 3–7 times their running wattage for the first second or two of startup. Size generators and extension cords for this starting surge, not just the running load.
1 kWh = 1 kW running for exactly 1 hour. A 100 W bulb running for 10 hours consumes 1 kWh. This is the unit your electricity bill uses. Multiply your appliance wattage by hours of daily use to estimate monthly kWh.
Check voltage compatibility before using appliances abroad. US appliances run at 120 V; European appliances run at 230 V. Many modern devices are dual-voltage (check the label for '100–240 V'); others require a transformer, not just a plug adapter.

Putting a petrol car's power output on the same scale as an electric vehicle's.

Calculating the minimum generator capacity to run essential appliances during a power outage.

List every appliance you need to run simultaneously.
Find the wattage of each (on the appliance label or in the manual).
Sum all wattages to find total running load.
Multiply by 1.5 to account for motor startup surges and leave headroom.
Convert the result to kW if needed using the Power Converter, then choose a generator rated at or above this figure.

Finding out how much it costs to run a specific appliance every month.

Find the appliance's wattage rating (on the label or manual).
Estimate daily hours of use.
Calculate daily kWh: (watts ÷ 1000) × hours per day.
Multiply by 30 for monthly kWh.
Multiply by your electricity rate (e.g. $0.13/kWh): a 1,500 W space heater running 4 hours/day costs approximately $7.80/month at $0.13/kWh.

Reading an industrial motor specification from a country that uses kW and converting to hp.

Find the kW rating on the motor's nameplate.
Open the Power Converter.
Enter the kW value, set From to 'kW' and To to 'hp'.
The hp equivalent appears — useful for matching the motor to US equipment specifications or replacement motor stock.

Checking whether a US appliance is equivalent to a European one when spec sheets use different units.

Note the wattage or power ratings from both spec sheets.
If one is in BTU/hr (e.g. an HVAC unit), convert to watts using the Power Converter.
If one is in hp (e.g. a workshop tool), convert to kW.
With both in watts or kW, you can directly compare output capacity.

Preventing overheating and fire risk from undersized extension cords.

Find your appliance's wattage from its label.
Divide by the mains voltage (120 V in the US, 230 V in Europe) to get the current in amps: amps = watts ÷ volts.
Check the extension cord's ampere rating (printed on its label or packaging).
The cord's rating must equal or exceed the appliance's current draw.
For appliances over 1,500 W, use a heavy-duty cord rated for 15 A or more.