• ⚡ Ohm's Law Calculator

    Calculate voltage, current, resistance, and electrical power using Ohm's Law. Enter any two known values and the calculator will solve for the remaining values automatically.
    Enter Any Two Known Values
    Electrical potential difference in volts.
    Electrical current in amperes.
    Electrical resistance or simplified resistive load in ohms.
    Electrical power in watts.

    Electrical Results

    Calculated Result —
    Voltage —
    Current —
    Resistance —
    Power —
    Ohm's Law Formula Reference
    Voltage
    V = I × R
    Voltage
    V = P ÷ I
    Voltage
    V = √(P × R)
    Current
    I = V ÷ R
    Current
    I = P ÷ V
    Current
    I = √(P ÷ R)
    Resistance
    R = V ÷ I
    Resistance
    R = V² ÷ P
    Resistance
    R = P ÷ I²
    Power
    P = V × I
    Power
    P = V² ÷ R
    Power
    P = I² × R
    Symbol Measurement Unit
    V Voltage Volt (V)
    I Current Ampere (A)
    R Resistance Ohm (Ω)
    P Power Watt (W)
    Important: Basic Ohm's Law calculations assume a resistive relationship between voltage, current, and resistance. Audio speakers, inductors, capacitors, motors, and many AC circuits can behave as reactive loads. In those cases, impedance, phase, frequency, RMS values, and other electrical properties may need to be considered.
    How does the Ohm's Law Calculator work?

    Ohm's Law describes the relationship between voltage, current, and resistance in an electrical circuit.

    The basic relationship is:

    V = I × R

    where V is voltage in volts, I is current in amperes, and R is resistance in ohms.

    Electrical power can also be included:

    P = V × I

    By combining these equations, voltage, current, resistance, or power can be calculated when two appropriate values are known.
    Tip: For speaker and amplifier calculations, remember that a speaker's nominal impedance is not the same as a fixed resistor. A speaker labeled 8 Ω can have a different impedance at different frequencies. Basic Ohm's Law is still useful for understanding electrical relationships, but real audio systems may require impedance and AC measurements for more precise calculations.

  • An Ohm's Law Calculator helps you calculate the relationship between voltage, current, resistance, and electrical power. It can be useful for audio systems, speaker projects, amplifiers, electronics, DIY circuits, automotive electrical systems, and general electrical calculations.

    Enter any two known values, and the calculator will determine the other two.

    The four main electrical measurements are:

    Voltage (V) — Electrical potential difference, measured in volts.

    Current (I) — The flow of electrical charge, measured in amperes or amps.

    Resistance (R) — Opposition to electrical current, measured in ohms (Ω).

    Power (P) — The rate at which electrical energy is transferred or consumed, measured in watts.

    Ohm's Law describes the basic relationship between voltage, current, and resistance:

    V = I × R

    For example, if 12 volts are applied across a 6-ohm resistance, the current is:

    I = 12 ÷ 6 = 2 amps

    Electrical power can also be calculated using:

    P = V × I

    In the same example:

    12 V × 2 A = 24 watts

    The calculator can rearrange these relationships automatically. You can enter voltage and resistance, current and resistance, voltage and current, resistance and power, or another supported pair without manually selecting which formula to use.

    Ohm's Law and Audio Equipment

    Ohm's Law is especially useful when working with speakers, amplifiers, and other audio equipment.

    For example, voltage and nominal speaker impedance can be used to estimate current and electrical power. Likewise, known amplifier power and load impedance can be used to estimate the corresponding RMS voltage and current for a simplified resistive load.

    However, a loudspeaker labeled 8 ohms is not a fixed 8-ohm resistor. Loudspeakers have electrical impedance that changes with frequency because the voice coil and mechanical speaker system form a reactive load.

    Because of this, basic Ohm's Law calculations using a speaker's nominal impedance should be treated as useful approximations rather than a complete model of real loudspeaker behavior.

    The same consideration applies to AC circuits containing capacitors and inductors, where impedance and phase can become important.

    Ohm's Law Formula Reference

    Several useful electrical formulas can be derived from Ohm's Law and the electrical power equation:

    Voltage: V = I × R, V = P ÷ I, or V = √(P × R)

    Current: I = V ÷ R, I = P ÷ V, or I = √(P ÷ R)

    Resistance: R = V ÷ I, R = V² ÷ P, or R = P ÷ I²

    Power: P = V × I, P = V² ÷ R, or P = I² × R

    These formulas make the calculator useful even when the two electrical values you already know vary from one project to another.

    Tip: When working with audio equipment, make sure you know whether a specification refers to DC resistance, nominal speaker impedance, or an AC impedance measurement. They are related concepts, but they are not always interchangeable. For speaker systems, use the manufacturer's nominal impedance and power specifications when checking amplifier compatibility, and use this calculator as an electrical reference rather than a substitute for the equipment manufacturer's limits.

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