Power Conversion Calculator
Our free electrical & magnetic converter handles power conversion conversions. See tables, ratios, and examples for quick reference.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator
Power Conversion Calculator
Calculator
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Formula: Converted Value = Input x (From Factor / To Factor) | dBm = 10 x log10(P_mW)
Worked example โ 5 hp = 3728.5 W = 3.73 kW = 12,723 BTU/h
Formula
Converted Value = Input x (From Factor / To Factor) | dBm = 10 x log10(P_mW)
Power conversion uses the watt as the base SI unit. Linear units convert by multiplying by the source factor and dividing by the target factor. The dBm scale is logarithmic: dBm = 10 x log10(power in milliwatts). Each 3 dB increase doubles the power, and each 10 dB increase multiplies power by 10.
Worked Examples
Example 1: Motor Power Rating
Problem:A motor is rated at 5 mechanical horsepower. Convert to watts, kilowatts, and BTU/h.
Solution:Watts = 5 x 745.7 = 3728.5 W Kilowatts = 3728.5 / 1000 = 3.7285 kW BTU/h = 3728.5 x 3.41214 = 12,723 BTU/h This is a typical small industrial motor rating.
Result:5 hp = 3728.5 W = 3.73 kW = 12,723 BTU/h
Example 2: Wireless Signal Power
Problem:A Wi-Fi router transmits at 20 dBm. What is this in watts and milliwatts?
Solution:P_mW = 10^(20/10) = 10^2 = 100 mW P_W = 100 / 1000 = 0.1 W 20 dBm is the typical maximum allowed power for Wi-Fi in many countries.
Result:20 dBm = 100 mW = 0.1 W
Frequently Asked Questions
What is a watt and how does it relate to other power units?
A watt (W) is the SI unit of power, defined as one joule per second. It measures the rate of energy transfer or conversion. One watt equals the power produced when one ampere of current flows through one volt of potential difference (P = V x I). Common multiples include kilowatts (1 kW = 1000 W) for household appliances, megawatts for power plants, and milliwatts for electronic signals. The watt is named after Scottish inventor James Watt.
What is the difference between mechanical, electrical, and metric horsepower?
Mechanical (imperial) horsepower equals 745.7 watts and was defined by James Watt based on the power output of draft horses. Electrical horsepower is exactly 746 watts by convention, used for rating electric motors. Metric horsepower (PS or CV) equals 735.5 watts, defined as the power to lift 75 kilograms one meter per second. The differences are small but matter in precise engineering calculations and legal motor specifications.
How do I convert watts to BTU per hour?
To convert watts to BTU per hour, multiply by 3.41214. To convert BTU/h to watts, divide by 3.41214 (or multiply by 0.29307). For example, a 1500 W space heater produces about 5118 BTU/h. This conversion is essential in HVAC engineering where heating and cooling capacity is specified in BTU/h in the US but watts or kilowatts in most other countries. One ton of refrigeration equals 12,000 BTU/h or about 3517 W.
What is dBm and how does it relate to watts?
dBm is a logarithmic power unit referenced to one milliwatt (mW). The conversion formula is dBm = 10 x log10(P_mW), where P_mW is power in milliwatts. So 0 dBm equals 1 mW, 10 dBm equals 10 mW, 20 dBm equals 100 mW, and 30 dBm equals 1 watt. Negative dBm values represent sub-milliwatt powers. dBm is widely used in telecommunications, RF engineering, and fiber optics because it simplifies gain and loss calculations to addition and subtraction.
How do significant figures affect unit conversions?
Your converted result should have the same number of significant figures as your original measurement. If you measure 5.2 inches (2 significant figures), converting to centimeters gives 13 cm, not 13.208 cm. Using excessive decimal places implies false precision.
What are the most common unit conversion mistakes?
Common errors include confusing fluid ounces with weight ounces, mixing up miles and nautical miles, forgetting that UK and US gallons differ (UK is 20% larger), using the wrong temperature formula, and not accounting for the difference between troy and avoirdupois ounces.
How precise should my unit conversions be?
Match precision to your application. Cooking tolerates rough conversions (1 cup is about 240 mL). Engineering may need 4-6 decimal places. Scientific work requires exact conversion factors and proper significant figure handling. More precision than your measurement accuracy is meaningless.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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