Watt Converter
Convert power between watts, horsepower, BTU per hour, kcal per hour and decibel units, or add a dB gain or loss to a signal level.
🔌 What is a Watt Converter?
A watt converter changes a power figure from one unit to another. The watt (W) is the SI unit of power, defined as one joule of energy transferred per second. Power is quoted in many other units depending on the trade: engines in horsepower, heating and air conditioning in BTU per hour, nutrition and combustion in kilocalories per hour, power stations in megawatts and gigawatts, and radio, Wi-Fi and fibre-optic links in decibel units such as dBm. This converter handles all of them, and it shows the same power in every unit at once in a table, so you can read the answer in the unit your datasheet or manual uses.
The page covers two jobs. The first is plain unit conversion. Enter a value, choose the unit it is in, choose the unit you want, and read the result. The second is decibel work. A level in dBm or dBW is a logarithmic measure of power, and engineers add and subtract decibels to account for amplifier gain or cable loss. Decibel mode converts a signal level to milliwatts and watts, applies a gain or loss, and plots the power curve on a log scale so you can see where the input and output sit. It differs from a general work and power calculator, which solves P = W/t, and from the work, energy and power calculator, which relates power to kinetic and potential energy.
Three details cause most conversion mistakes. First, there are three horsepowers: mechanical (745.6999 W, equal to 550 ft lbf/s), metric PS (735.49875 W, equal to 75 kgf m/s) and electrical (exactly 746 W). Second, BTU/h and kcal/h are rates, while a BTU or a kilocalorie alone is energy, so you cannot convert a plain BTU to watts without a time. Third, decibels are not linear: adding 10 dB multiplies power by 10, and 0 dBm is 1 mW, not zero power. Zero watts has no decibel value at all.
This tool uses the International Table BTU (1055.05585 J) and the thermochemical kilocalorie (4184 J). It is for conversion and estimation. For electrical loads see the AC wattage calculator, and for heat produced in a resistor use the power dissipation calculator.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — One Mechanical Horsepower in kW
Convert 1 mechanical horsepower to kilowatts
Example 2 — A One-Ton Air Conditioner
An air conditioner is rated 12000 BTU/h. How many kW is that?
Example 3 — A Cable Loss on a 20 dBm Signal
A 20 dBm transmitter feeds a cable that loses 3 dB
Example 4 — A Wi-Fi Router at 100 mW
A router transmits 100 mW. What is that in dBm and dBW?
Example 5 — A 1 kW Heater in Other Units
Express 1000 W as kilocalories per hour
❓ Frequently Asked Questions
🔗 Related Calculators
How many watts are in one horsepower?
One mechanical horsepower is 745.6999 W, which is 550 foot-pounds force per second. Metric horsepower (PS) is 735.49875 W and electrical horsepower is defined as 746 W. For quick estimates 1 hp is about 0.75 kW.
How do I convert watts to BTU per hour?
Multiply watts by 3.41214. One watt equals 3.41214 BTU/h (International Table BTU), so a 1500 W heater puts out about 5118 BTU/h. To go the other way, multiply BTU/h by 0.29307.
How do I convert dBm to watts?
Use P(W) = 0.001 x 10^(dBm/10). 0 dBm is 1 mW, 20 dBm is 100 mW, 30 dBm is exactly 1 W and 40 dBm is 10 W. Negative dBm values are fractions of a milliwatt, so -30 dBm is 1 microwatt.
What is the difference between dBm and dBW?
Both are power levels in decibels. dBm is referenced to 1 milliwatt and dBW to 1 watt. Because 1 W is 1000 mW, a level in dBW is 30 less than the same level in dBm: 30 dBm equals 0 dBW.
How many kW is 1 hp?
One mechanical horsepower is 0.7457 kW. One metric horsepower is 0.7355 kW. Going the other direction, 1 kW is 1.34102 mechanical hp or 1.35962 metric hp.
How many watts is 12000 BTU/h?
12000 BTU/h is 3516.85 W, or 3.51685 kW. This is exactly one ton of refrigeration in air conditioning, so a 1 ton air conditioner removes heat at about 3.5 kW.
What is a watt in simple terms?
A watt is one joule of energy transferred per second. A 60 W bulb converts 60 joules of electrical energy every second. The unit is named after James Watt and is the SI unit of power.
Can power be negative in this converter?
Not in linear units. A power in W, kW or hp is entered as zero or more. Decibel levels (dBm and dBW) can be negative, because they describe a ratio to a reference, and a level below the reference is negative.
How do I add a loss in dB to a signal level?
Subtract the loss from the level. A 20 dBm signal through a 3 dB cable loss becomes 17 dBm, or about 50.12 mW. Gains are added in the same way, which is why engineers use decibels for link budgets.
Is a kilowatt-hour a power unit?
No. A kilowatt-hour is energy, equal to 3.6 million joules. A kilowatt is power. If an appliance draws 2 kW for 3 hours it uses 6 kWh.