Watt Converter - Watts, Horsepower, and BTU/h
Watt converter for engineering and physics. Translate any power value between watts, kilowatts, horsepower, BTU/h, and milliwatts with NIST-traced factors.
Watt Converter
Results
What Is Watt Converter?
A watt converter is a small power unit tool that takes a single value expressed in any common power unit and shows the equivalent value in every other supported unit at the same time. Type in 1500 W, pick watts as the source unit, and the calculator returns kilowatts, megawatts, milliwatts, mechanical, electric, and metric horsepower, BTU per hour, and foot-pounds per second so the result lines up with whichever spec sheet or motor nameplate is being read.
- • Coursework and Lab Reports: Physics and engineering students translate problem values between watts, kilowatts, and horsepower to match the units in their textbook or assignment.
- • Motor and Appliance Spec Sheets: Electricians, technicians, and homeowners compare a motor nameplate in HP or kW with the watt rating printed on a circuit or a generator spec sheet.
- • HVAC and Thermal Equipment: HVAC contractors and energy auditors convert air conditioner cooling capacity from BTU/h to thermal watts, then divide by the unit's EER or COP to estimate the actual electrical draw they need to size a circuit for.
- • Renewable Energy Sizing: Solar installers and off-grid planners move between milliwatts, watts, kilowatts, and megawatts for sensor datasheets, panel ratings, and utility-scale arrays.
Watt conversion is a scaling operation, not a measurement. The watt is the SI unit of power, and every other unit on this page is a fixed multiple of the watt defined by NIST, ISO, or the equivalent standards body. A single input drives the whole panel.
When the watt value needs to be combined with a time interval or a force times distance to compute work or energy, work-energy-power calculator shows the full work-energy-power triangle alongside the same power unit.
How Watt Converter Works
The watt converter reads one number and one source unit, converts that number into watts using the matching SI or standards-body factor, and then divides the watt value by the factor of every target unit to fill the results panel.
- sourceValue: Numerical value in the selected source unit. Combined with sourceUnit, this drives the entire conversion. Positive numbers only.
- sourceUnit: Unit the source value is expressed in. Watts, kilowatts, megawatts, milliwatts, gigawatts, mechanical HP, electric HP, metric HP, BTU per hour, or foot-pounds per second.
SI prefixes (kilo-, mega-, giga-, milli-) use exact 10^n factors defined by the BIPM SI Brochure, so a kilowatt is exactly 1000 watts and a megawatt is exactly 1,000,000 watts. The horsepower, BTU/h, and ft-lb/s factors come from NIST Special Publication 811.
Worked example: 1500 W space heater
sourceValue = 1500, sourceUnit = w.
value_in_watts = 1500 * 1 = 1500 W. kilowatts = 1500 / 1000 = 1.5 kW. hpMech = 1500 / 745.6999 = 2.0115 hp. btuPerHour = 1500 / 0.2931 = 5117.71 BTU/h.
1500 W = 1.5 kW = 2.0115 mechanical HP = 2.0107 electric HP = 2.0394 metric HP = 5117.71 BTU/h = 1,500,000 mW.
A 1500 W space heater draws the same power as a 1.5 kW circuit load, just over 2 mechanical horsepower of heating output, and roughly 5118 BTU/h of thermal capacity.
According to BIPM SI Brochure, the watt is the SI derived unit of power, defined as one joule per second, which makes it the natural anchor unit for any power conversion.
According to NIST Special Publication 811, mechanical horsepower is defined as 550 foot-pounds per second, electric horsepower is exactly 746 watts, and one International Table BTU per hour equals approximately 0.2931 watts.
When the watt value comes from a gravitational or elastic system where energy is converted into power over time, potential energy calculator shows the energy side of the same physical setup the watt converter is measuring.
Key Concepts Explained
Four small concepts explain what a watt actually is, why horsepower comes in three flavors, and how to read the results panel without confusing watts with joules.
Watt as the SI Anchor
The watt is the SI derived unit of power, defined as one joule per second. Every other power unit on this page is a fixed multiple of the watt, which is why a single input value drives the entire results panel.
Three Horsepower Flavors
Mechanical horsepower equals about 745.7 W, electric horsepower is exactly 746 W for motor ratings, and metric horsepower (PS) is 735.49875 W for European engines. The standards differ by up to 1.4 percent.
SI Scaling Prefixes
Kilo- is 10^3, mega- is 10^6, giga- is 10^9, and milli- is 10^-3. Each prefix multiplies the watt by an exact power of ten, so conversions stay exact at every scale.
Power vs Energy
Power is the rate of energy use in watts. Energy is the total work done over time, in joules, watt-hours, or BTU. A 1500 W heater consumes 1500 joules every second it runs.
One useful sanity check: the same watt value should produce the same answer in every unit. A 1500 W input that reads 1.5 kW should also read 0.0015 MW and 1,500,000 mW. If two outputs disagree, the input unit or the conversion factor is wrong, not the panel itself.
When the watt reading describes a moving mass where kinetic energy is converted into mechanical power, kinetic energy calculator translates the same mass and velocity into joules so the watt panel and the energy panel use the same numbers.
How to Use This Calculator
Five short steps take you from a single power value to a complete row of equivalent readings in every supported unit.
- 1 Find the Source Value: Locate the power rating you want to convert. It might come from a motor nameplate in HP, a generator spec in kW, an air conditioner label in BTU/h, or a sensor datasheet in mW.
- 2 Pick the Source Unit: Select the unit that matches the source value from the dropdown. The selector covers watts, kilowatts, megawatts, gigawatts, milliwatts, three horsepower flavors, BTU per hour, and foot-pounds per second.
- 3 Enter the Number: Type the value into the power value field. The calculator accepts any positive number and updates every output as soon as the input or the unit changes.
- 4 Read the Primary Watt Result: The watts card at the top of the results panel shows the SI value. Read this first to confirm the conversion happened on the right unit before reading the derived rows.
- 5 Scan the Other Units: Use the kilowatts, horsepower, BTU/h, and milliwatts rows to match whichever spec sheet or reference table you started with. No extra clicks or unit switches required.
Imagine translating a 110 kW industrial motor nameplate for a spec sheet written in horsepower and BTU per hour. Pick kilowatts as the source unit, type 110, and read the watts card (110,000 W), the mechanical HP card (about 147.5 hp), and the BTU/h card (about 375,299 BTU/h).
When the watt reading feeds a circuit calculation that needs the underlying joule and voltage pair, joules to volts calculator converts energy and charge into the voltage drop the watt converter result needs to size a wire.
Benefits of Using This Calculator
A focused watt converter removes the conversion table from the desk and lets the user read the equivalent value in every standard power unit at once.
- • Single Entry Drives Every Output: Type one value once and read watts, kilowatts, megawatts, gigawatts, milliwatts, three horsepower flavors, BTU/h, and ft-lb/s from the same panel.
- • Standards-Body Conversion Factors: Uses the NIST-defined horsepower and BTU/h factors and the SI prefix values, so the output matches engineering references and manufacturer spec sheets.
- • Covers All Three Horsepower Standards: Returns mechanical, electric, and metric horsepower at once, removing the trap of confusing a 746 W electric rating with a 745.7 W mechanical rating.
- • Bridges Power and HVAC Units: Reads BTU/h and foot-pounds per second alongside the watt output, useful for sizing air conditioners, heaters, and mechanical drives without a separate thermal converter.
- • Scales From Milliwatts to Gigawatts: Handles a sensor mW reading and a utility-scale GW capacity in the same panel, covering electronics coursework and large-scale generation planning.
The biggest practical benefit is consistency. A spec sheet that mixes SI and imperial units can be reconciled in one row of outputs without retyping the input or remembering which direction the conversion goes.
Factors That Affect Your Results
Five practical factors shape the value that ends up on a nameplate or a spec sheet, and knowing them helps the user pick the right conversion factor for the right standard.
Which Horsepower Standard
The same engine can show three different horsepower numbers depending on the standard. A 1500 W engine is about 2.0115 mechanical hp, 2.0107 electric hp, or 2.0394 metric PS. Choosing the wrong standard shifts the rating by up to 1.4 percent.
SI Prefix Magnitude
Watts, kilowatts, megawatts, and gigawatts are the same unit at different scales. A 500 MW power plant is the same as 0.5 GW and 500,000 kW, but mixing them up can move the decimal point by three or six places.
Thermal vs Mechanical Power
BTU/h describes thermal power and ft-lb/s describes mechanical power. Both go through the watt anchor, but the practical reading differs because the source unit comes from a different physical context.
Continuous vs Peak Rating
Manufacturers often print a continuous power rating and a short-term peak rating on the same nameplate. The continuous rating is the safe value for circuit sizing, while the peak rating matters for inrush and surge planning.
Efficiency Losses
Real machines never convert 100 percent of input power into useful output. A motor that draws 110 kW from the line might deliver 100 kW at the shaft, with the rest lost as heat. The converter translates numbers exactly, but the user applies efficiency separately.
- • The watt converter only translates between linear power units. dBm (decibel-milliwatts) is logarithmic and needs a separate logarithmic conversion, so it is intentionally excluded from this panel.
- • Reactive and apparent power (VAR and VA) describe AC circuits and are not the same as real power in watts. The converter should not be used to translate kVA into kW without a power factor correction applied separately.
For most coursework and spec-sheet work, the watt anchor is enough. The values match what NIST and ISO publish, and the rounding is consistent across all rows. The watt anchor breaks down only when the source unit is logarithmic or describes a different physical quantity, and those cases are out of scope.
According to ISO 1000, metric horsepower (PS) equals 735.49875 watts, which is the rating European manufacturers print on engines, motors, and pumps and which the calculator uses as the metric horsepower anchor.
When the watt reading is paired with motor speed and torque to size a mechanical drive, torque power speed calculator shows the torque-speed-power triangle that pairs with this tool for shaft-side efficiency calculations.
Frequently Asked Questions
Q: How do you convert watts to kilowatts?
A: Divide the watt value by 1000 to get kilowatts, or multiply the kilowatt value by 1000 to get watts. A 1500 W space heater is the same as 1.5 kW, and a 5000 W electric cooktop is 5 kW. The factor is exact because the SI prefix kilo- multiplies a unit by exactly 10^3.
Q: How many watts are in one horsepower?
A: One mechanical horsepower equals approximately 745.7 watts, one electric horsepower equals exactly 746 watts, and one metric horsepower (PS) equals 735.49875 watts. The mechanical and electric values are within 0.04 percent of each other; the metric value is about 1.4 percent lower than the imperial values.
Q: How do you convert BTU per hour to watts?
A: Multiply BTU/h by approximately 0.2931 to get thermal watts, or divide watts by 0.2931 to get BTU/h. A 10,000 BTU/h window AC delivers about 2931 W (roughly 0.83 tons) of cooling capacity, not wall draw; divide cooling watts by the unit's EER to estimate actual electrical input. A 1500 W resistive space heater converts to about 5118 BTU/h of thermal output.
Q: What is the difference between mechanical, electric, and metric horsepower?
A: Mechanical horsepower (hp or hp(I)) is defined as 550 foot-pounds per second, about 745.7 W. Electric horsepower (hp(E)) is exactly 746 W and is used for electric motor nameplates. Metric horsepower (PS or hp(M)) is exactly 735.49875 W and is the rating used across continental Europe.
Q: How do you convert milliwatts to watts?
A: Divide the milliwatt value by 1000 to get watts, or multiply the watt value by 1000 to get milliwatts. A 500 mW sensor reading is the same as 0.5 W, and a 2 W Bluetooth transmitter is the same as 2000 mW. The factor is exact because the SI prefix milli- divides a unit by exactly 10^3.
Q: How many watts are in one BTU per hour?
A: One International Table BTU per hour equals approximately 0.2931 watts. The watt value is small because a BTU is a small unit of thermal energy, and dividing it by an hour produces a small rate.