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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

What is an acceptable voltage drop according to electrical codes?
The National Electrical Code (NEC) includes an informational note (NEC 210.19(A) Note 2) suggesting that branch circuit voltage drop should not exceed 3%, and total combined feeder plus branch circuit voltage drop should not exceed 5%. These are recommended design guidelines for efficiency and equipment life rather than mandatory code violations.
Why does single-phase use a factor of 2 while three-phase uses √3?
In a single-phase circuit, current must complete a round-trip loop traveling out on the hot wire and back through the neutral, covering twice the one-way distance (2 × L). In a balanced three-phase circuit, the return currents cancel at the neutral point, so the line-to-line voltage drop calculation uses the trigonometric phase factor √3 (≈ 1.732).
Does temperature affect wire resistance and voltage drop?
Yes. Conductor resistance increases as copper heats up. Our calculator uses resistance data from NEC Chapter 9, Table 8 evaluated at 75°C (167°F), which represents typical operating temperatures under load.
How do I fix a circuit that has excessive voltage drop?
The most direct solution is to increase the wire size to a thicker gauge (for example, stepping up from 14 AWG to 12 AWG or 10 AWG). Decreasing the length of the run or reducing the connected load will also lower voltage drop.
Are voltage drop calculator outputs considered code compliant?
No. Online calculators provide engineering estimates. Real installations require evaluating conduit fill derating, ambient temperature correction factors, continuous load duty cycles, and local jurisdiction amendments.
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 🔌2 Gauge Wire ⚡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.

📚 Cite & Reference This Calculator

Verified Standard Calculation

Need to cite this calculator for academic papers, engineering notes, or school assignments? Use the reference below:

OnlineConvers. (2026). Voltage Drop Calculator. Retrieved from https://www.onlineconvers.com/electrical/voltage-drop-calculator