Voltage Drop Calculator 2026 | Free Cable & Wire Size Tool

⚡ Electrical Engineering Tool — 2026 Updated

Voltage Drop Calculator

Calculate voltage drop in copper, aluminum, and steel cables. Supports AWG, mm², NEC and IEC standards, single-phase and 3-phase systems.

🔌 Copper / Aluminum / Steel 📏 AWG & mm² ⚡ 3-Phase & Single-Phase 📊 NEC & IEC Standards

⚡ Voltage Drop Calculator

Enter your electrical parameters and get instant voltage drop results

🔧 Cable Material

⚡ System Type

📊 Voltage (V)

⚡ Current (A)

📏 Cable Length (m)

📐 Cable Size

📋 Standard

🌡️ Temperature (°C)

📊 Voltage Drop

2.48 V

2.48V drop — 1.08% of 230V — ✅ Acceptable (NEC <3%)

Resistance

0.248 Ω

Power Loss

24.8 W

Status

✅ PASS

⚡ What is Voltage Drop?

📖 Definition

Voltage drop is the reduction in voltage along the length of a conductor caused by the resistance of the wire. When current flows through a cable, some voltage is lost as heat due to the cable's inherent resistance. A voltage drop calculator helps determine if a cable is suitable for a specific application.

Whether you're an electrical engineer, electrician, or DIY enthusiast, this cable voltage drop tool simplifies complex calculations.

⚡ Why Voltage Drop Matters

Equipment Performance: Low voltage can cause motors to overheat, lights to dim, and equipment to malfunction
Energy Efficiency: Excessive voltage drop wastes energy as heat in the cable
Safety: Undersized cables can overheat and cause fire hazards
Code Compliance: Most electrical codes limit voltage drop to 3-5%

📐 Voltage Drop Formula

Single-Phase (AC / DC)

V_drop = 2 × I × R × L

3-Phase (AC)

V_drop = √3 × I × R × L

Where: I = Current (A), R = Resistance per meter (Ω/m), L = Length (m)

📊 Conductor Resistivity Table

Material	Resistivity at 20°C (Ω·m)	Temperature Coefficient	Common Uses
Copper	1.68 × 10⁻⁸	0.00393 /°C	Residential, commercial wiring
Aluminum	2.65 × 10⁻⁸	0.00403 /°C	Overhead lines, large feeders
Steel	1.0 × 10⁻⁷	0.00450 /°C	Railway, grounding, structural

📋 NEC & IEC Voltage Drop Guidelines

🇺🇸 NEC (USA)

Branch circuits: 3% maximum drop
Feeders: 3% maximum drop
Total (feeder + branch): 5% maximum
NEC 210.19(A)(1) and 215.2(A)(1)

🌍 IEC (International)

Luminaires: 3% maximum
Other equipment: 5% maximum
IEC 60364-5-52

🇬🇧 BS 7671 (UK)

Lighting: 3% maximum
Power: 5% maximum
BS 7671:2018+A2:2022

📖 How to Use This Calculator

Step 1: Select Cable Material

Choose between copper (most common), aluminum (lighter), or steel (specialized). The calculator uses the correct resistivity for each material.

Step 2: Enter System Parameters

Input your system voltage, current, cable length, and system type (single-phase, 3-phase, or DC). Select the cable size and standard.

Step 3: Get Instant Results

The calculator instantly shows the voltage drop in volts and percentage, along with the status (Pass/Fail) based on the selected standard.

🔧 Real-World Examples

🏠 Residential (USA)

System: Single-phase 120V, 15A, 50ft, Copper #12 AWG
Result: 1.85V drop (1.54%) ✅ PASS
Application: General household circuits

🏭 Industrial (3-Phase)

System: 3-phase 480V, 100A, 150m, Aluminum 35mm²
Result: 13.2V drop (2.75%) ✅ PASS
Application: Motor feeders

🇬🇧 UK Lighting Circuit

System: Single-phase 230V, 6A, 80m, Copper 1.5mm²
Result: 4.8V drop (2.1%) ✅ PASS
Application: Lighting circuits (BS 7671)

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❓ Frequently Asked Questions

What is voltage drop?

Voltage drop is the reduction in voltage along the length of a conductor caused by the resistance of the wire. It is calculated as Vdrop = I × R × L for DC and single-phase AC, and Vdrop = √3 × I × R × L for 3-phase AC.

What is the acceptable voltage drop limit?

NEC recommends 3% for branch circuits and 5% total (feeder + branch). IEC and BS 7671 recommend 3% for lighting and 5% for other equipment.

How do I reduce voltage drop?

Increase cable size (lower resistance), reduce cable length, increase system voltage, or reduce current by distributing loads across multiple circuits.

What cable material is best for minimizing voltage drop?

Copper has the lowest resistivity (1.68×10⁻⁸ Ω·m), making it the best conductor for minimizing voltage drop. Aluminum has about 60% higher resistance, and steel has about 600% higher resistance.

What is the difference between AC and DC voltage drop calculation?

DC uses Vdrop = 2 × I × R × L. AC single-phase uses the same formula. 3-phase uses √3 × I × R × L. AC systems may also have impedance effects at high frequencies.

How do I calculate voltage drop for a 3-phase system?

For 3-phase systems, use the formula: Vdrop = √3 × I × R × L. For example, at 480V, 100A, 150m, Aluminum 35mm², the voltage drop is approximately 13.2V (2.75%).

Does voltage drop affect LED lighting?

Yes! LED lighting is sensitive to voltage drop. Even a small drop can reduce brightness and cause flickering. Use larger cables or shorter runs for LED installations.

How do I use the voltage drop calculator on this page?

Select your cable material, system type, enter voltage, current, length, cable size, standard, and temperature. Click 'Calculate Voltage Drop' to get instant results including voltage drop in volts, percentage, resistance, power loss, and pass/fail status.

🌍 International Users: If you're in the UK, you might also find our WASPI Compensation Calculator helpful for pension planning. For weather-related electrical safety, check the Snow Day Predictor to plan your outdoor electrical work.

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