Physics Converter
Convert force, energy, and power units accurately — no sign-up, no data sent to a server.
What this converter handles
Physics units don't always translate neatly between disciplines — a mechanical engineer thinks in kilowatts, a nutritionist in kilocalories, and a physics student in joules. This tool bridges those worlds across three physical domains:
Force
Newtons (N), Kilonewtons, Pound-force (lbf), Dyne
Used in structural analysis, automotive specs, and mechanical design.
Energy
Joules, Kilojoules, Calories, Kilocalories, kWh, BTU, eV
Spans thermodynamics, nutrition science, and electrical engineering.
Power
Watts, Kilowatts, Megawatts, Horsepower (hp), BTU/hr
From household appliances to turbine output ratings.
Who uses it — and why
The converter is deliberately broad because these conversions come up across very different contexts:
Mechanical & Automotive Engineers
Engine datasheets often list output in kW (metric) or hp (imperial). If you're specifying a drivetrain component or comparing motors from different manufacturers, switching between the two is a daily friction. One conversion click removes it.
Nutritionists & Dietitians
Food labels in Europe display energy in kilojoules, while clients think in kilocalories (kcal). The relationship is fixed — 1 kcal = 4.184 kJ — but having it on-hand matters when you're working through a client's meal plan or checking imported product labels.
Physics & Engineering Students
Textbooks mix SI and non-SI units constantly, especially when drawing from older sources. Converting pound-force to Newtons or BTUs to joules in the middle of a problem set is something this tool handles in seconds.
HVAC & Energy Consultants
Thermal load calculations frequently involve BTUs per hour and watts in the same document. Getting the arithmetic right matters when sizing equipment — a mistake of even 10% can mean an undersized system.
Science Communicators & Educators
Explaining that a lightning bolt releases roughly 1 billion joules, or that a human at rest produces about 80 watts, lands differently when you can quickly pull the equivalent in more familiar units for your audience.
Practical examples
Knowing the conversion factor is useful — knowing what the result means is more useful. Here are a few real-world contexts to calibrate your results:
| Scenario | Input | Output |
|---|---|---|
| Car engine rating | 150 hp | 111.85 kW |
| Food label reading | 2,000 kJ | 477.9 kcal |
| Solar panel output | 400 W | 0.4 kW |
| Structural bolt load | 500 lbf | 2,224.1 N |
| AA battery capacity | 4,500 J | 1.25 Wh |
Tips for accurate results
Horsepower has variants
Mechanical hp (745.7 W), metric hp (735.5 W), and electrical hp (746 W) are all slightly different. This converter uses mechanical horsepower by default — the standard in automotive contexts.
Calories vs. kilocalories
Nutrition labels use kilocalories (kcal), often written as just "Calories" with a capital C. If you're converting food energy, make sure you're entering kcal, not cal — the difference is a factor of 1,000.
Watch your decimal separator
Some countries use a comma (1.000,5) where others use a period (1,000.5). This tool expects standard decimal notation with a period as the decimal separator.
Power ≠ Energy
A 2,000 W heater running for 1 hour uses 2 kWh of energy. Power tells you the rate; energy tells you the total. If you're calculating electricity bills or battery runtime, you'll need both.
Limitations to keep in mind
This tool handles unit conversion — it does not model physical systems. A few things it won't do:
- —Calculate efficiency losses. Converting kW to hp assumes ideal conditions; real motors lose 5–20% to heat and friction.
- —Handle context-dependent units like BTU/lb or specific energy. Those require additional material properties.
- —Account for temperature-dependent calorie values. The "thermochemical calorie" (4.184 J) and the "15°C calorie" (4.18580 J) differ slightly — relevant only in precision calorimetry.
- —Perform multi-step formula calculations (e.g., power from force × velocity). For that, you'd need a physics calculator.
Frequently asked questions
What's the difference between energy and power?
Energy is the total amount of work done or heat transferred — it's measured in joules, kilocalories, or kilowatt-hours. Power is how fast that energy flows — measured in watts or horsepower. Think of energy as a bucket of water and power as the rate you're pouring it.
How many watts are in one horsepower?
One mechanical horsepower equals exactly 745.699872 watts. In practice, most engineers round this to 746 W. Metric horsepower (PS), used in some European vehicle ratings, is slightly lower at 735.5 W.
Why do food labels use kilojoules and kilocalories at the same time?
EU regulations require both on packaged food. Kilojoules are the SI unit; kilocalories (Calories) are the unit most people recognize from daily life. They measure the same thing — 1 kcal = 4.184 kJ.
Is the conversion done locally or sent to a server?
All conversions happen entirely in your browser using JavaScript. No values you enter are transmitted anywhere — there's no API call, no logging, and no session stored.
Can I use this for academic or professional work?
Yes. The conversion factors used are the internationally accepted SI-defined values. For publication or certification work, you may want to cite the original standards (NIST SP 811 or ISO 80000), but the numbers themselves are identical.