V · I · R · P
Ohm’s Law Power Calculator
Calculate electrical power from voltage, current or resistance. Explore worked formulas, power curves, resistor loading, comparisons and energy use over time.
The three panels are independent and always visible. Enter two known magnitudes in a panel; all results and substitutions update as you type. Positive resistance is required. The V–I panel needs both values positive to derive a finite positive resistance.
P = V × I
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Power
Formula and calculation
P = I²R
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Power
Formula and calculation
P = V²/R
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Power
Formula and calculation
Power versus voltage · Power versus current
Resistance stays fixed. Both P(V) = V²/R and P(I) = I²R are quadratic. Each slider explores a point on its curve without changing the calculation panels. Axis units and upper limits are shown explicitly.
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Power versus voltage
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Power versus current
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Resistor power design
Choose the reference calculation, nominal resistor rating and target utilization from above 0% to 100%. Limits follow from the selected power allowance and resistance; a negative margin means the target is exceeded. These are model limits, not certified safe operating limits.
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Formula and calculation
The percentage compares calculated dissipation with the rating you enter; it is not a safety approval. Check the component datasheet, ambient temperature, mounting conditions and derating. Operating below the label rating alone does not guarantee suitability.
Compare two power values
Both values are expressed in watts before comparison. Difference means B − A; percentage change is relative to A. If A is zero, a ratio and percentage change are undefined. No performance or efficiency ranking is inferred.
Configuration A
Configuration B
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Formula and calculation
Energy over time
At constant power, E = P × t. kW measures power; kWh measures energy. Enter nonnegative power and time. The line is a constant-power model, not a prediction of changing real-world consumption. When time is zero, energy is zero.
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Formula and calculation
Model and limitations
This is a steady-state DC model of a positive, constant, ohmic resistance. Values are nonnegative magnitudes. It does not model AC impedance, component temperature or installation safety.
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