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Voltage Drop Calculator

Enter a circuit's current, cable length and cross-section, and material to see the voltage drop in volts and as a percentage.

Tool statusRuns in your browser
Preview
!
Voltage drop alone doesn't size a conductor.

Current-carrying capacity, temperature, installation method, grouping, protection, short-circuit withstand, and local codes also need checking. Treat this as a design estimate, not installation approval.

prontouso://electrical/voltage-drop
ΔV · LOAD · SECTIONAUTOMATIC UPDATE

Circuit data

Start with the circuit type and the load.

INPUT
Circuit type

The length entered is one-way only; the return path is factored into the calculation.

How do you want to enter the load?
A
V
m
%

The limit is adjustable because design criteria and codes vary by country, circuit, and application.

Conductor material
Cable cross-section
mm²
Technical adjustments
°C
Ω/km

Resistance is approximately corrected for temperature. Reactance is optional and only affects AC circuits when power factor is below 1.

LOCAL ESTIMATE · NO LOGIN

Circuit diagnosis

Drop, voltage at the load, and comparison against your limit.

RESULT
VOLTAGE DROPABOVE THE LIMIT
ESTIMATED DROP
3.45%

The estimated drop exceeds the design limit of 3.0%. Voltage at the load lands at roughly 222.1 V.

7.93 V
lost along the circuit
REVIEW THE SECTION
222.07 VESTIMATED VOLTAGE AT THE LOAD
0.8621 ΩPATH RESISTANCE
10.00 ACURRENT USED IN THE CALCULATION
Drop margin3.45% OF 3.00%
3.45%
3.00% · LIMIT
lower drophigher drop

This bar only compares the calculated drop with the configured limit — it isn't ampacity or code compliance.

First standard section that meets the limitBY VOLTAGE DROP
ESTIMATED MINIMUM SECTION
6 mm²

Among the standard sections compared, 6 mm² is the first that keeps the drop within the chosen limit.

DROP WITH THIS SECTION2.30%
COMPARISON2.5 mm²5.52% · 217.3 V
CURRENT4 mm²3.45% · 222.1 V
MEETS LIMIT6 mm²2.30% · 224.7 V
MEETS LIMIT10 mm²1.38% · 226.8 V
See formula and assumptions
ΔV = 2 × I × L × (R·cosφ + X·sinφ)

In single-phase, the tool accounts for the round trip. Resistance is estimated from copper's resistivity corrected to 20 °C.

How it works

  1. Enter your input

    Fill in the values, paste your text, or upload the file this tool works with.

  2. See results instantly

    Most tools update live as you type; a few use a single button. Either way, the result appears right on this page.

  3. Use your results

    Copy, download, or share what the tool produces — you're always in control of the output.

Privacy and processing — Runs locally in your browser. This tool does not upload your input.

What is Voltage Drop Calculator?

The Voltage Drop Calculator is a tool for estimating voltage loss along a single-phase, three-phase, or DC cable run from current (or power), length, material, cross-section, and conductor temperature — including power factor and reactance for AC circuits — and it recommends the first standard cable section that keeps the drop within your chosen limit.

UNDERSTAND THE TOOL

How to calculate voltage drop for single-phase, three-phase, and DC circuits

Pick the circuit type, enter the load as current or power, the one-way length, the material, and the cable cross-section to see the drop in volts and as a percentage, the estimated voltage at the load, and the first standard section that meets your design limit.

Three circuit types, three formulas

"One-way length" is always the distance from source to load, never round-trip — the tool applies the factor for the circuit type you chose on its own.

Direct current
ΔV = 2 × I × L × ρ(T) / S
Single-phase
ΔV = 2 × I × L × (R·cosφ + X·sinφ)
Balanced three-phase
ΔV = √3 × I × L × (R·cosφ + X·sinφ)

Enter the load as current or as power

In "Current" mode, type the measured or design current directly in amps. In "Power" mode, enter the active power (W), the source voltage, the power factor (cos φ), and the efficiency (η) — useful when all you have is a piece of equipment's rated power, such as a motor's nameplate, instead of a measured current; the tool estimates the equivalent current before calculating the drop. The voltage shortcuts (127, 220, 230, 380, 400, and 440 V) fill in the most common single-phase and three-phase supply voltages.

Power factor and reactance: when they change the result

Power factor (cos φ) and the approximate reactance (Ω/km, under "Technical adjustments") only affect single-phase and three-phase circuits, and only when the power factor is below 1 — in that case the drop adds a resistive and a reactive share. Direct current locks the power factor to 1 automatically once you switch the circuit type, and leaving reactance at 0 Ω/km makes the calculation use only the resistive drop.

Temperature correction: resistance isn't fixed

The copper or aluminum resistivity used in the calculation is corrected from the conductor's operating temperature entered under "Technical adjustments" (20 °C by default, adjustable from -20 °C to 150 °C) — a hotter conductor has more resistance, and for the same current, more voltage drop.

Recommended section: the tool tests the whole list of standard gauges

The "First standard section that meets the limit" card evaluates a list of commercial cross-sections, from 1.5 to 240 mm², under the same current, length, material, and temperature you entered, and flags the first (smallest) section whose drop stays within your configured design limit — alongside a comparison of the standard sections closest to the one you typed, marking which ones meet the limit. If no section up to 240 mm² qualifies, the tool says so instead of suggesting a value.

The margin gauge and the configurable limit

The "Design limit" is adjustable from 0.1% to 20% (3% by default) because design criteria and codes vary by country, circuit type, and application. The margin bar only compares the calculated drop against that limit — the "comfortable margin", "tight margin", and "review the section" states don't represent the cable's current-carrying capacity or compliance with any specific code.

A design estimate, not full sizing

The calculation runs entirely in your browser from the values you enter — nothing is sent to a server. Voltage drop is only one variable in an electrical design: the cable's current-carrying capacity, ambient temperature, installation method, circuit grouping, short-circuit protection, and local codes also need to be checked by a professional before any installation is approved.

Frequently Asked Questions

Current or power: which mode should I use?

Use Current when you know the circuit's measured or design current. Use Power when all you have is the equipment's rated power — for example, on a motor's nameplate — along with the power factor and efficiency; the tool estimates the equivalent current before calculating the drop.

What changes between single-phase, three-phase, and DC?

Each uses a different formula: single-phase and DC apply a factor of 2 (current travels out and back through the conductor); three-phase uses a factor of √3, reflecting how line-to-line voltage relates to per-phase current in a balanced load. In DC, the power factor is always locked to 1.

Is the length I enter one-way or round-trip?

Always one-way — from source to load. The tool applies the round-trip factor (single-phase or DC) or the √3 factor (three-phase) on its own; don't double the value yourself.

When does reactance actually change the result?

Only in AC circuits (single-phase or three-phase) and only when the power factor is below 1. With reactance at 0 Ω/km or the power factor at 1, the calculation uses only the resistive drop.

Why does conductor temperature affect the drop?

Because a conductor's resistance rises with temperature. The tool corrects copper or aluminum resistivity from the temperature you enter (20 °C by default); a hotter conductor has more resistance, and for the same current, more voltage drop.

How is the recommended section chosen?

The tool tests a list of standard gauges (from 1.5 to 240 mm²) under the same current, length, material, and temperature, and flags the first (smallest) section whose drop stays within your configured limit — it isn't necessarily the technically ideal gauge for current-carrying capacity or short-circuit withstand, only for voltage drop.

Copper or aluminum — which has less drop?

Copper, for the same cross-section — it has roughly 60% of aluminum's resistivity at 20 °C, so a copper run of the same gauge drops noticeably less voltage than an aluminum one.

Does this tool replace full electrical design?

No. It calculates voltage drop only; the cable's current-carrying capacity, grouping, ambient temperature, short-circuit protection, and local codes also need to be checked by a professional before any real installation.

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