12
V
12,000
mV
0.012
kV
24
W
24
J/s
12
V
12,000
mV
0.012
kV
24
W
24
J/s
The Voltage Calculator computes the voltage drop across a resistive element using Ohm's Law:
$$V = I \times R$$
where V is voltage in volts (V), I is current in amperes (A), and R is resistance in ohms (Ω). Voltage, also called electromotive force (EMF) or potential difference, is the electrical pressure that drives current through a circuit.
Voltage is analogous to water pressure in a pipe — it provides the force that pushes electrons through conductors. A higher voltage across the same resistance results in proportionally more current, as Ohm's Law dictates. The volt is named after Alessandro Volta, who invented the first electrochemical battery in 1800.
Calculating voltage drops is critical for circuit design. In a series circuit, the total supply voltage divides among components proportionally to their resistances. If the voltage drop across a component is too high, other components may not receive sufficient voltage to operate correctly. This is especially important in long cable runs where wire resistance causes significant voltage drop.
The NEC recommends that voltage drop in branch circuits not exceed 3% (5% total including feeder). For a 120 V circuit, the maximum acceptable drop is 3.6 V. Exceeding this causes dimming of lights, reduced motor torque, and overheating of equipment attempting to draw more current to compensate.
Kirchhoff's Voltage Law (KVL) states that the sum of all voltage drops around any closed loop equals zero — meaning the source voltage exactly equals the sum of drops across all components. This principle, combined with V = IR, forms the foundation of mesh analysis used to solve complex circuits.
This calculator also displays results in millivolts (mV) for low-voltage sensor applications and kilovolts (kV) for power transmission contexts, along with the associated power dissipation (P = I²R) and energy transfer rate.
For AC circuits, voltage can be expressed as peak, peak-to-peak, or RMS (root mean square). The RMS value, equal to the peak value divided by √2, is the equivalent DC voltage that produces the same heating effect and is the standard measurement for AC power systems.
Enter the current flowing through the circuit and the resistance of the element. The calculator multiplies them (V = IR) to determine the voltage drop. Results appear in volts, millivolts, and kilovolts. Power dissipation is calculated as P = I²R, which equals the energy converted to heat per second (joules per second = watts).
The calculated voltage represents the potential difference required to push the specified current through the given resistance. In a series circuit, ensure the sum of individual voltage drops does not exceed your supply voltage. For cable runs, keep the voltage drop below 3% of the supply voltage for optimal performance.
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A 15 A load through 0.2 Ω of wire resistance produces a 3 V drop. On a 120 V circuit, this is 2.5% — within the NEC 3% recommendation. The wire dissipates 45 W as heat.
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A 10 mΩ current shunt carrying 10 A produces V = 10 × 0.01 = 100 mV. This voltage is measured by a meter to display current. The shunt dissipates 1 W and needs adequate heat sinking.
Voltage (V) is the electrical potential difference between two points, measured in volts. It represents the energy per unit charge (1 V = 1 J/C) and is the driving force that pushes current through a circuit. Sources of voltage include batteries, generators, and power supplies.
KVL states that the algebraic sum of all voltages around any closed loop in a circuit equals zero. In practice, the supply voltage equals the sum of all voltage drops: V_source = V₁ + V₂ + V₃ + ... This is the basis for series circuit analysis.
Wires have resistance proportional to their length and inversely proportional to their cross-sectional area: R = ρL/A. Current flowing through this resistance creates a voltage drop (V = IR), reducing the voltage available at the load. Thicker wires (lower AWG) have less resistance and less voltage drop.
The NEC (National Electrical Code) recommends a maximum 3% voltage drop for branch circuits and 5% total (feeder + branch). For a 120 V system, this means no more than 3.6 V drop in the branch circuit or 6 V total from the panel to the outlet.
EMF (electromotive force) is the voltage generated by a source (battery, generator) with no load. Voltage drop is the potential difference across a component due to current flow. Under load, the terminal voltage equals EMF minus the internal voltage drop: V_terminal = EMF − I × r_internal.
In a parallel circuit, the voltage across all parallel branches is the same and equals the source voltage. Current divides among branches, but voltage remains constant. This is why household outlets (parallel connections) all provide the same 120 V regardless of load.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
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