Primary formula
P = W / t; P = E / t; P = F x v x cos(theta).
Physics calculator
Power Calculator
Calculate power as a rate of doing work or transferring energy. The calculator also supports force times velocity for aligned mechanical motion.
Last reviewed: July 21, 2026Physics mechanics engine v1.0.0
Physics calculator
Power Calculator
Enter values, select units and calculate locally. Results use SI internally and show rounded display values.
Decimal.js physics math
Mode
Find power from work and elapsed time.
Result and visual stay hidden until you choose Calculate.
Formula and assumptions
Input assumptions
Time is greater than zero. Force and velocity are aligned unless an angle is entered. Results may be average power.
Precision note
Physics Phase 1 converts compatible inputs into SI units before calculating. Decimal.js is used for arithmetic where practical; trigonometric angle factors are rounded for display.
Physics calculation flow
Parse
Read labelled inputs, selected units and calculation mode from the calculator card.
Convert
Convert compatible values to SI base or derived units without calling external services.
Calculate
Apply the selected deterministic mechanics formula and validate against NaN, Infinity and invalid divisors.
Label
Display the result, supporting unit rows, formula steps, warnings and dynamic visual below the input card.
What Power Calculator does
Use this when the question asks for watts, kilowatts or horsepower from a formula relationship.
The calculator is deterministic and runs from manual inputs only. It is a physics formula tool, so it should not be confused with a unit converter that only changes labels after a value is already known.
Formula and variables
P = W / t; P = E / t; P = F x v x cos(theta).
The calculator converts supported units into SI base or derived units for the actual calculation, then formats the result in the selected display unit.
- P is power
- W is work
- E is energy
- t is time
- F is force
- v is velocity or speed
Worked examples
Use the examples below to check expected order of operations and unit handling before applying the tool to your own values.
- 500 J / 10 s = 50 W
- 100 N x 2 m/s = 200 W
- 0.2 kWh / 2 h = 100 W
Unit conversions
Length, time, mass, speed, force, energy and power units reuse the central NexaCalc conversion registry. Acceleration and spring-constant units use the same SI-first convention for mechanics formulas.
The displayed conversion rows are supporting context. They do not change the physical assumptions of the selected formula.
Common mistakes
Most errors come from mixing physical quantities that sound similar in everyday language or choosing a unit that belongs to a different dimension.
- Mixing up kW and kWh.
- Using zero time.
- Ignoring the force-velocity angle.
Assumptions and limitations
This page is intended for educational and planning calculations, not professional engineering certification.
This calculator uses idealized physics formulas and the input values you provide. Real systems may require additional effects such as friction, drag, rotation, deformation, losses or measurement uncertainty.
- Time is greater than zero.
- Force and velocity are aligned unless an angle is entered.
- Results may be average power.
- The calculator does not include motor efficiency, heat loss or variable power curves.
- Use Power Converter when only unit conversion is needed.
Frequently asked questions
How do you calculate power from work and time?
Power Calculator uses P = W / t; P = E / t; P = F x v x cos(theta). The result is calculated from the values and units entered in the form.
What is the difference between power and energy?
Power Calculator is formula-based. Use the related calculator when the question changes physical quantity, and use Conversion tools only when the value is already known.
Why is watt equal to joule per second?
Power Calculator converts compatible inputs to SI internally, then displays the selected output unit. P is power; W is work; E is energy; t is time; F is force; v is velocity or speed.
How do I calculate work from power and time?
Power Calculator uses P = W / t; P = E / t; P = F x v x cos(theta). The result is calculated from the values and units entered in the form.
How is power related to force and velocity?
Use this when the question asks for watts, kilowatts or horsepower from a formula relationship. Time is greater than zero.
Is kW the same as kWh?
Power Calculator is formula-based. Use the related calculator when the question changes physical quantity, and use Conversion tools only when the value is already known.
What does average power mean?
Use this when the question asks for watts, kilowatts or horsepower from a formula relationship. Time is greater than zero.
Does this calculator include efficiency losses?
Power Calculator uses an idealized classroom mechanics model. The calculator does not include motor efficiency, heat loss or variable power curves.
When should I use Power Converter?
Use this when the question asks for watts, kilowatts or horsepower from a formula relationship. Time is greater than zero.
How is horsepower related to watts?
Power Calculator converts compatible inputs to SI internally, then displays the selected output unit. P is power; W is work; E is energy; t is time; F is force; v is velocity or speed.
References
- NIST Special Publication 811, Guide for the Use of the International System of Units. Relevance: SI unit symbols and derived-unit naming. Last verified: July 21, 2026. Source.
- BIPM, The International System of Units SI Brochure. Relevance: SI base and derived units used in mechanics. Last verified: July 21, 2026. Source.
- OpenStax University Physics Volume 1. Relevance: introductory mechanics formulas for motion, force, work, energy and momentum. Last verified: July 21, 2026. Source.
Physics Phase 1 references verified for SI units and mechanics formulas on July 21, 2026.
Educational disclaimer
This calculator provides mathematical results from the values, conventions and methods you enter. Verify important academic, engineering or professional work independently.