Voltage Drop Calculator

Romik Amreliya

Calculate voltage drop across electrical wiring to ensure safe and efficient power delivery.

Source Voltage (V)

Current (Amps)

Wire Length (meters, one way)

Wire Gauge (mm²)

Wire Material

Phase

What is Voltage Drop?

Voltage drop is the decrease in electrical potential as current flows through a wire. All conductors have resistance, which causes some voltage to be "lost" as heat. Excessive voltage drop can cause equipment malfunction, dim lights, motor overheating, and wasted energy. Proper wire sizing ensures efficient and safe power delivery in any electrical installation.

Voltage Drop Formula

VD = (2 × ρ × L × I) / A

VD = Voltage drop · ρ = Resistivity (Ω·mm²/m) · L = One-way length (m) · I = Current (A) · A = Cross-section area (mm²)

For three-phase systems, the factor 2 is replaced by √3 (1.732). The resistivity (ρ) depends on the wire material: copper has ρ = 0.0175 Ω·mm²/m, while aluminum has ρ = 0.0283 Ω·mm²/m.

Step-by-Step Example

Example: 15A Load, 30m Copper Wire, 2.5mm², Single Phase, 230V

Step 1: Identify values — ρ = 0.0175, L = 30m, I = 15A, A = 2.5mm²

Step 2: Apply formula — VD = (2 × 0.0175 × 30 × 15) / 2.5

Step 3: VD = 15.75 / 2.5 = 6.3V

Step 4: Drop % = (6.3 / 230) × 100 = 2.74%

End Voltage: 230 – 6.3 = 223.7V

This is within the acceptable 3% range ✓

Acceptable Voltage Drop Standards

NEC (US) standard: Maximum 3% for branch circuits, 5% total (feeder + branch)
IS 732 (India): Maximum 5% for lighting, 5% for power circuits
Below 2%: Excellent — minimal power loss
2-3%: Acceptable for most applications
3-5%: May cause issues with sensitive equipment
Above 5%: Not recommended — equipment may malfunction

Wire Sizing Guide

If your voltage drop is too high, you can reduce it by:

Using a larger wire gauge: Doubling the cross-section area halves the voltage drop. Upgrading from 2.5mm² to 4mm² reduces drop by 37.5%.
Reducing cable length: Place panels and distribution boards closer to the load.
Using copper instead of aluminum: Copper has 38% less resistance than aluminum.
Reducing current: Use more efficient equipment or split the load across multiple circuits.

Real-Life Use Cases

Home wiring: Ensure your air conditioner, water heater, or kitchen appliances receive adequate voltage at the outlet despite long wire runs.
Solar panel installations: Calculate wire sizes for DC runs from solar panels to the inverter, where every volt matters for efficiency.
Industrial applications: Size feeder cables for motors and machinery in factories where wire runs can be 100+ meters.
Outdoor lighting: Garden and landscape lighting often requires long cable runs — proper sizing prevents dim lights at the far end.

Frequently Asked Questions

Use larger wire gauge, shorten cable runs, increase voltage, or reduce current load. Keeping voltage drop under 3% for branch circuits is recommended.

Copper has lower resistivity than aluminum, meaning less voltage drop for the same wire size. However, aluminum is lighter and cheaper, making it suitable for larger installations.

Wire gauge depends on current, distance, and acceptable voltage drop. Use this calculator to find the optimal gauge for your specific installation requirements.

RA

Written & Reviewed by Romik Amreliya

Software Engineer & Data Analyst. Dedicated to building precise, privacy-first web calculators based on standardized financial and medical algorithms. All tools and content undergo rigorous testing against industry-standard benchmarks.

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Safety Disclaimer: This voltage drop calculator is for educational and estimation purposes only. Always consult a licensed electrician and follow local electrical codes (NEC, IS 732, IEC) for actual wire sizing. Improper wire sizing can cause fire hazards, equipment damage, and electrical shock.