If you’ve spent time sizing a motor or matching a drive, you already know how fast things get messy with power units. One spec sheet lists HP, another is in kW, then you see BTU/h in HVAC jobs. This calculator is here to sort that out so you can translate between horsepower, kilowatts, watts, BTU/h, ft⋅lb/s, and metric horsepower using one tool. Unit confusion isn’t a minor issue: get this wrong and you can end up with an undersized motor or incompatible system. Below, you’ll find the actual conversion formulas, an example, technical background, and a FAQ.
What is power unit conversion?
Power unit conversion means writing the same amount of power in whatever units the job or datasheet calls for—say, changing horsepower to kilowatts. The physical quantity is always the same; only the measuring stick changes. Accurate conversion lets you match specs between motors, drives, or systems, even if the paperwork uses different units.
Simple Explanation
Power is just how quickly work gets done—whether that’s burning fuel in a car or lifting a load with a motor. A “2 HP” label, “1.5 kW” listing, or “5,118 BTU/h” all describe the same thing but use different terms. This calculator saves you from hunting down conversion factors every time.
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Power Conversion Diagram
Power Unit Converter Calculator
How to Use This Calculator
This calculator is intended for education, concept evaluation, and preliminary design. Results are based on the equations and assumptions described on this page, but cannot account for every real-world load case, tolerance, material property, environmental condition, installation detail, safety factor, code, or regulatory requirement. Verify all inputs, assumptions, units, and results independently before selecting components or using the result in a real application. Safety-critical, structural, medical, lifting, transportation, or regulated applications must be reviewed by a qualified engineer.
- Enter your known power value in the Power Value field.
- Select the unit you are converting from using the From Unit dropdown — choose HP, kW, W, BTU/h, ft⋅lb/s, or PS.
- Review the input to confirm the value and unit match your source data.
- Click Calculate to see your result.
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Power Unit Converter Interactive Visualizer
Use this visualizer to see how changing an input value or unit adjusts the equivalent outputs in real time. It’s handy for a quick gut check or sanity check between HP, kW, Watts, and BTU/h—especially when sorting through conflicting specs.
HORSEPOWER
13.4 HP
KILOWATTS
10.0 kW
BTU/H
34,121 BTU/h
FIRGELLI Automations — Interactive Engineering Calculators
Power Conversion Equations
The easiest way to convert is to get everything into watts first, then convert to whatever unit you need. Here’s how:
Base Conversion Factors to Watts:
Pwatts = PHP × 745.699872
Pwatts = PkW × 1000
Pwatts = PBTU/h × 0.293071
Pwatts = Pft⋅lb/s × 1.355818
Pwatts = PPS × 735.49875
Common Direct Conversions:
- 1 HP = 0.7457 kW = 745.7 W = 2544.4 BTU/h
- 1 kW = 1.341 HP = 1000 W = 3412.1 BTU/h
- 1 PS = 0.9863 HP = 0.7355 kW = 735.5 W
Simple Example
Input: 2 HP (horsepower)
Watts: 2 × 745.699872 = 1,491.40 W
Kilowatts: 1.4914 kW
BTU/h: 1,491.40 ÷ 0.293071 = 5,088.8 BTU/h
Metric HP (PS): 1,491.40 ÷ 735.49875 = 2.027 PS
Complete Guide to Power Unit Conversions
Understanding Power Units
Power is simply how fast energy moves or work gets done—energy per time. The units covered here are the ones you’ll actually see in mechanical drives, electric motors, HVAC, and automation. Knowing how to translate between them isn’t an academic thing; if you’re building or specifying gear, you’ll run into this.
The basic math linking power, work, and time is:
Power = Work ÷ Time = Force × Velocity
Common Power Units Explained
Watts (W) - The SI Base Unit
Watt is the go-to SI unit for power—one joule of energy moved in one second (1 W = 1 J/s). You’ll see watts on electrical power ratings and small motors. It’s the basis for most conversions.
Kilowatts (kW) - Industrial Standard
One kilowatt is 1,000 watts. This is standard on most industrial motors, drives, heaters, and bigger appliances. Datasheets for linear actuators and motors are often in kW or W, so day-to-day conversions are straightforward if you stick to these.
Horsepower (HP) - Mechanical Power
Horsepower stuck around from the steam engine days and is still common for motors, pumps, and compressors, especially in the US and some industrial settings. One HP is exactly 745.699872 watts. Watch out—HP and metric HP aren’t quite the same.
BTU per Hour (BTU/h) - Thermal Applications
BTU/h is what you’ll see in heating and cooling jobs. One BTU/h is about 0.293 watts. If you’re switching between mechanical power and thermal ratings—say, in HVAC sizing—this conversion is constant work.
Metric Horsepower (PS)
Metric horsepower (Pferdestärke, PS) is 735.49875 watts. Mostly it pops up on European equipment or older car specs, so convert carefully—using HP when you mean PS (or vice versa) will throw things off by a percent or two.
Practical Applications and Examples
Motor Selection and Sizing
If you’re picking a motor for an automation job and the requirement is “2 HP,” but everything you’re sourcing lists kW or W, you need a reliable conversion. For example, 2 HP = 1.491 kW, or 1,491 W. Having direct numbers makes it much easier to do load calculations, fuses, and wiring.
Energy Consumption Analysis
Power conversion isn’t just for up-front sizing. If you run a 5 kW motor for 8 hours, that’s 40 kWh. If you need this in HP (for legacy reports or old specs), that’s 6.71 HP—so you’re communicating the same job in the units your audience expects.
HVAC System Design
Heating and cooling specs are all over the place—some use BTU/h, others stick to kW. If a system is rated at 12,000 BTU/h, you’re dealing with about 3.516 kW. Being able to quickly shift between these is necessary for picking the right units and checking estimates.
Worked Example: Linear Actuator System Design
Here's a practical sizing job for a linear actuator:
Given:
- Required force: 500 lbf
- Operating speed: 2 inches per second
- System efficiency: 80%
Step 1: Calculate required mechanical power
Power = Force × Velocity
Power = 500 lbf × 2 in/s = 1,000 lbf⋅in/s
Convert to ft⋅lb/s: 1,000 ÷ 12 = 83.33 ft⋅lb/s
Step 2: Adjust for efficiency
Input power = 83.33 ÷ 0.80 = 104.17 ft⋅lb/s
Step 3: Convert to electrical units
104.17 ft⋅lb/s × 1.356 = 141.25 watts = 0.141 kW = 0.189 HP
This gets you close to the size of motor and driver you actually need to spec for real-world operation.
Design Considerations and Best Practices
Safety Factors
Add a buffer—usually 20-50% above your duty power. This is for transients, load spikes, unknown friction, and rounding out the unexpected. If things are critical, go higher and check system derating for environmental conditions.
Efficiency Considerations
Formulas assume 100% efficiency, but reality isn’t so kind. Most electric motors are in the 80-95% range, and mechanical linkages can range from 70-90%. Remember to factor in these losses when sizing or comparing systems.
Peak vs. Continuous Power
Motors and drives are often rated with both peak and continuous numbers. Don’t mix them up. Systems will survive short overloads, but the continuous figure is the one to use for steady-state specs.
Environmental Factors
Temperature, altitude, and humidity change what a motor or actuator can really deliver. Higher temps or working at altitude? Expect to have to derate. Always check the fine print if you’re near the limits.
Integration with Automation Systems
In real automation, you end up with a mix of datasheets—one lists watts, another HP or PS. Converting everything up front means fewer headaches when matching systems or troubleshooting power problems. Account for how the actuator is actually used: repeated cycles might need a bigger motor than occasional moves.
Check how duty cycle affects power and thermal limits. If your system runs intermittently, you might not need the largest available motor, but for continuous or high-frequency use, you’ll want more capacity. Converters like this streamline back-and-forth between different manufacturers’ specs.
Advanced Applications
Variable Frequency Drives (VFDs)
If you’re dealing with VFDs, you’ll need to translate your load (maybe in HP) to kW, since drives are almost always specified this way. Always size the VFD to handle both running and starting loads—err on the side of more margin rather than less.
Power Quality and Harmonics
Don’t forget that real versus apparent power matters, especially in AC systems with low power factor or high THD. This converter just handles the physics—the actual watts. For real installations, make sure you address power factor separately in your calculations.
Renewable Energy Systems
Renewable sources like solar or wind are rated in watts, but sometimes need interfacing with legacy equipment in HP. This conversion tool gives you the grounding needed to size storage, inverters, and hybrid systems with confidence—just keep efficiency losses in mind.
Measurement and Verification
After installing a system, check that actual power draw is in line with what was calculated. Use actual measurement tools—don’t trust the spec sheet when troubleshooting. If there’s a big mismatch, something’s off: check for binding, bad bearings, or wrong connections. Catching even small deviations early often saves real headaches later on.
Power measurements can also help diagnose whether issues are electrical (like low power factor), mechanical (like excessive load), or system-wide. Regularly checking readings against your design numbers is just good practice.
Frequently Asked Questions
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About the Author
Robbie Dickson
Chief Engineer & Founder, FIRGELLI Automations
Robbie Dickson brings over two decades of engineering expertise to FIRGELLI Automations. With a distinguished career at Rolls-Royce, BMW, and Ford, he has deep expertise in mechanical systems, actuator technology, and precision engineering.
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