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Home › Wire Gauge Calculators › Voltage Drop Calculator

Voltage Drop Calculator

Calculate voltage drop across a wire run — enter gauge, length, current, and system voltage.

Electrical
One-way run length in feet
Load current in amperes
Source voltage (e.g. 120, 240, 208, 480)
Formula
V_drop = K × I × L / CM
K = 12.9 (copper) or 21.2 (aluminum) for single-phase; multiply by √3 ≈ 1.732 for 3-phase. I = current (A), L = one-way length (ft), CM = circular mils of the wire.

Voltage Drop

— V

 

Calculation Breakdown

DETAILED RESULTS

ParameterValue
Receiving Voltage—

About Voltage Drop Calculator

The NEC recommends keeping total voltage drop below 3% for branch circuits and 5% total (feeder + branch). This calculator uses the circular-mil method (V = K × I × L / CM) — the same method used by licensed electricians and NEC Chapter 9 tables. Copper K = 12.9, Aluminum K = 21.2 for single-phase; multiply by √3 for three-phase.

ℹ️ About Voltage Drop Calculator

The Voltage Drop Calculator converts Amps/Length/Wire to V Drop instantly and accurately. Whether you're sizing electrical equipment, designing circuits, or checking power requirements, this tool gives you fast, reliable results.

📋 How to Use

  1. Enter the value in Amps/Length/Wire.
  2. Enter any other required values (voltage, power factor, etc.).
  3. Click Calculate to convert to V Drop.
  4. Read the result and use the formula shown for manual verification.

🔢 Formula / Calculation Method

V Drop = (2 × L × I × R) ÷ 1,000

R is resistance per km/mile of wire at the given gauge.

👥 Who Uses It

  • Electricians
  • Engineers
  • Solar installers
  • Contractors
  • Building inspectors

📌 Practical Examples

Amps/Length/Wire Input
Enter Amps/Length/Wire value and required parameters.
Result
Instantly see the equivalent V Drop value.
Circuit Sizing
Use the result to size wires, breakers, or equipment.
Verification
Cross-check manual calculations.

⭐ Benefits

⚡
Fast
Instant conversion results
🎯
Accurate
Industry-standard formulas
📱
Mobile
Works on any device
🔢
Formula
See the math behind results
🆓
Free
No cost or login
🌍
Universal
Works for any voltage system

💡 Tips

  • 💡Always enter the correct voltage (120V, 220V, 240V, 480V etc.) for your system.
  • 💡For 3-phase systems, use the 3-phase formula option if available.
  • 💡Power factor is typically 0.8–0.95 — use 0.85 if unsure.
  • 💡Always verify calculated values against local electrical codes (NEC, IEC).

❓ Frequently Asked Questions

How do I convert Amps/Length/Wire to V Drop?
Use the formula: V Drop = (2 × L × I × R) ÷ 1,000
What voltage should I use?
Use your system voltage — 120V or 240V for US residential, 230V for UK/EU.
What is power factor?
Power factor (0–1) represents how efficiently power is used. Use 0.8 as a safe default.
Is the calculator accurate?
Yes, it uses standard electrical engineering formulas.
Is it free?
Yes, completely free.
Should I rely on this for wiring?
Always verify with a licensed electrician before making wiring decisions.
Does it support 3-phase?
Yes, select the 3-phase option if your system uses three-phase power.
What is the difference between kVA and kW?
kW is real power; kVA is apparent power. kW = kVA × Power Factor.

🔗 Related Calculators

⚡Ohm's Law ⚡Power Calculator ⚡Voltage Drop ⚡Amps to Watts ⚡Watts to kWh ⚡Wire Gauge

🚀 Features

⚡
Instant Results
Calculate in seconds, no waiting
🎯
High Accuracy
Precise results every time
📱
Mobile Friendly
Works on any device or screen size
🔒
Privacy First
No data stored or shared
🌍
Works Worldwide
Available 24/7 from anywhere
🆓
100% Free
Always free, no registration needed

⚠️ Common Mistakes to Avoid

  • ⚠️Using the wrong voltage (120V vs 240V) — this halves or doubles results.
  • ⚠️Ignoring power factor for AC circuits — can cause undersized equipment.
  • ⚠️Confusing single-phase and three-phase formulas.
  • ⚠️Using DC formulas for AC circuits without power factor adjustment.

📖 Glossary

Volt (V)
Unit of electrical potential — the 'pressure' that drives current.
Ampere (A)
Unit of electrical current — the 'flow rate' of electrons.
Watt (W)
Unit of real power — energy per unit time.
kVA
Kilo-Volt-Amperes — unit of apparent power in AC systems.
Power Factor
Ratio of real power to apparent power (0 to 1).
kWh
Kilowatt-hour — unit of energy consumed over time.

📢 Disclaimer

Electrical calculations are provided for reference only. Always consult a licensed electrician and verify against local electrical codes before making wiring or equipment decisions.