⚡ Voltage Drop Calculator
Calculate voltage drop in wires and circuits
How to Use This Calculator
Select Calculation Method
Choose to calculate using current and resistance (V = I × R) or using wire parameters (length, area, resistivity) which first calculates resistance then voltage drop.
Enter Current
Input the current flowing through the wire or circuit in Amperes. This is the current that causes the voltage drop.
Enter Resistance or Wire Parameters
If using resistance method, enter the total resistance. If using wire method, enter wire length, cross-sectional area, and material resistivity (default is copper).
Calculate
Click the "Calculate Voltage Drop" button to get the voltage drop in Volts. This represents the voltage lost across the wire resistance.
Formula
V = I × R
Voltage Drop (Ohm's Law)
R = ρL / A
Wire Resistance
Where:
- V = Voltage Drop (Volts, V)
- I = Current (Amperes, A)
- R = Resistance (Ohms, Ω)
- ρ = Resistivity (Ohm-meters, Ω⋅m)
- L = Wire Length (meters, m)
- A = Cross-Sectional Area (square meters, m²)
Example Calculation:
For I = 10 A, R = 0.1 Ω:
V = 10 × 0.1 = 1.0 V
Note: Voltage drop reduces voltage available at the load. Excessive voltage drop can cause equipment malfunction. Typically, voltage drop should be <3-5% of supply voltage for good performance.
About Voltage Drop Calculator
The Voltage Drop Calculator determines the voltage lost when current flows through a wire or circuit element with resistance. Voltage drop occurs due to wire resistance and can reduce the voltage available at loads. Excessive voltage drop can cause equipment malfunction, dim lights, and motor starting problems. This calculator helps ensure adequate voltage at loads.
When to Use This Calculator
- Wire Sizing: Determine appropriate wire gauge for circuits
- Circuit Design: Ensure adequate voltage at loads
- Electrical Installation: Verify voltage drop compliance
- Long Wire Runs: Calculate voltage drop in long cables
- Power Distribution: Analyze voltage regulation in systems
Why Use Our Calculator?
- ✅ Dual Methods: Calculate from resistance or wire parameters
- ✅ Quick Calculation: Instantly determine voltage drop
- ✅ Wire Sizing: Essential for proper circuit design
- ✅ Free Tool: No registration or payment required
- ✅ Educational: Learn about voltage drop and wire resistance
Common Applications
Wire Gauge Selection: Calculate voltage drop to select appropriate wire gauge for electrical circuits. Larger wire gauge (smaller AWG number) reduces resistance and voltage drop. Electrical codes typically limit voltage drop to 3-5% of supply voltage for branch circuits and feeders.
Long Cable Runs: Determine voltage drop in long cable installations, such as outdoor lighting, security systems, or remote equipment. Long wires have higher resistance, requiring larger wire gauge to maintain adequate voltage at the load. This calculator helps prevent voltage drop issues.
Motor Starting: Analyze voltage drop during motor starting, when starting current can be 5-7× normal current. High starting current causes significant voltage drop, potentially causing motors to fail to start or operate inefficiently. Proper wire sizing ensures adequate voltage during motor starting.
Tips for Best Results
- Voltage drop should be <3% for branch circuits, <5% for feeders
- Larger wire gauge (lower AWG number) reduces voltage drop
- For AC, consider both resistance and reactance (impedance)
- Multiply by 2 for two-wire circuits (out and return)
- Copper has lower resistivity than aluminum (better for voltage drop)
Frequently Asked Questions
What is voltage drop?
Voltage drop is the reduction in voltage that occurs when current flows through a wire or circuit element with resistance. According to Ohm's law (V = IR), voltage drop equals current times resistance. It reduces the voltage available at loads, potentially causing equipment problems.
Why is voltage drop important?
Excessive voltage drop can cause: dim lighting, motors failing to start, equipment malfunction, reduced efficiency, and overheating. Electrical codes typically limit voltage drop to 3-5% of supply voltage. For 120V circuits, this means maximum 3.6-6V drop.
How do I reduce voltage drop?
Use larger wire gauge (lower AWG number), shorter wire runs, or reduce current draw. Larger wire has lower resistance, reducing voltage drop. For a given current, doubling wire cross-sectional area halves resistance and voltage drop.
Do I need to multiply by 2 for voltage drop?
For two-wire circuits (single-phase AC or DC), yes - multiply resistance by 2 because current flows out on one wire and returns on the other, so both wires contribute to voltage drop. For three-phase circuits, calculate per phase.
How does wire gauge affect voltage drop?
Larger wire gauge (lower AWG number) has larger cross-sectional area, lower resistance, and less voltage drop. For example, 12 AWG has lower resistance than 14 AWG. Common gauges: 14 AWG (smallest), 12 AWG, 10 AWG, 8 AWG (larger).
Is voltage drop the same for AC and DC?
For DC and resistive AC loads, yes - use V = IR. For AC with reactive loads, impedance (Z) includes both resistance and reactance: V = IZ. At power frequencies (50-60 Hz), wire reactance is usually small, so resistance dominates for most applications.