Calculate voltage, current, resistance, and wattage in one step. Enter any two values to solve the rest, then read the guidance below to validate wiring, avoid voltage drop, and plan safe loads.
V = I * R (Voltage = Current / Resistance)
I = V / R (Current = Voltage / Resistance)
R = V / I (Resistance = Voltage / Current)
Input any two numbers for voltage, current, resistance, or power, and pick the correct units.
The calculator auto-selects the right formula (V = I × R or P = V × I) and handles unit conversions.
See the missing values in volts, amps, ohms, and watts plus the formulas used for transparency.
Compare current to breaker limits, check voltage drop, and ensure parts meet the calculated wattage.
Your output includes the missing electrical quantities in both the base unit and the unit you selected. Voltage is in volts (V), current in amperes (A), resistance in ohms (Ω), and power in watts (W). If you selected kilovolts, kilo-ohms, or milliwatts, the calculator scales values back before display.
Always compare the calculated current to the circuit/s breaker rating and conductor ampacity. For example, a Texas garage circuit often uses 20 A breakers. If your load calculates to 18 A, you are already at 90% of capacity, and voltage drop across long wire runs can nudge current higher.
Voltage drop check: on a 75 ft 12 AWG copper run carrying 15 A, the drop is about 2.4 V (roughly 2%). If your device is sensitive, step up to 10 AWG or shorten the run to keep voltage drop under 3% for good performance.
When power is high, evaluate heat: resistors and heating elements must dissipate watts safely. If the calculator shows 360 W on a resistor rated for 250 W, choose a higher wattage part or add heat sinking.
Ensure voltage is in volts (V), current in amperes (A), and resistance in ohms (Ω) for accurate calculations.
Temperature, material properties, and component tolerances can affect actual values in practical applications.
Always follow electrical safety protocols when working with live circuits and high voltages.
Don't confuse AC and DC calculations, and remember that Ohm's Law applies to resistive circuits primarily.
Ohm's Law links voltage (V), current (I), and resistance (R) with the core equation V = I * R. Rearranging yields I = V / R and R = V / I. Power ties in through P = V * I. With any two of these values, the others solve immediately.
For parallel circuits, remember that currents add while voltage stays the same. For series circuits, resistances add and current remains constant. Kirchhoff/s laws work alongside Ohm's Law to verify that the sum of voltage drops in a loop equals the source voltage.
Use the Ohm's Law wheel: upper ring shows V at the top, I and R at the bottom corners. Cover the variable you need, and the remaining arrangement shows whether to multiply or divide the other two values.
In AC systems, replace simple resistance with impedance (Z). If a load has 6 O resistance and 4 O inductive reactance, impedance is v(6/ + 4/) / 7.2 O. Using 120 V, current is 16.7 A instead of 20 A, and power factor is 0.83. Your wiring and breaker still need to handle the apparent current, not just real power.
Long runs in workshops or farms across states like Texas or Florida face heat and humidity that raise conductor resistance. Use the NEC voltage-drop guideline: keep combined feeder and branch drop under 5%. Upsize conductors one gauge when your calculated drop exceeds 3% on a dedicated branch.
If you work with generators, remember that surge wattage can be 2/ running watts. Use the calculator with the surge current to ensure cords and transfer switches stay within ampacity.
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Divide voltage by resistance: I = V / R. Enter those two numbers and the calculator returns current instantly.
Use R = V / I. If you know current draw and supply voltage, the calculator computes resistance and power together.
Cover the value you need. If voltage is covered, multiply current / resistance. If resistance is covered, divide voltage by current.
Yes. Power equals voltage times current (P = V * I). Enter V and I to see watts plus the remaining variables.
Currents are equal through all components. Add individual resistances, then apply V = I * R to the total.
Compute current using the LED forward voltage and desired current, then choose a resistor with at least 2/ the calculated wattage to run cool.
It works when you use impedance instead of resistance. Pair it with power factor to understand real versus apparent power.
The calculator returns resistance (R = V / I) and power (P = V * I) simultaneously, ideal for quick breaker checks.
Multiply current by wire resistance per foot and length, then subtract the drop from source voltage. Keep total drop under 3% for branch circuits.
Yes at operating temperature. However, cold resistance can be lower, so inrush current may be higher for the first few seconds.