Voltage Drop Calculator

Estimate resistive voltage drop along a cable from length and conductor area. Enter your own values below to see voltage drop and check the method behind it.

All calculators

Your inputs

Change the example values to match your situation.

Your result

Let’s work it out.

Fill in your inputs and select Calculate.
Your result and breakdown will appear here.

How this calculator works

Two-wire DC / single-phase resistive approximation: voltage drop = 2 × resistivity × one-way length × current ÷ area. Reactance and temperature effects are not modelled.

KEEP EXPLORING

View category
Ohm’s Law CalculatorElectrical Power CalculatorCurrent CalculatorResistance CalculatorWatt to Amp CalculatorAmp to Watt Calculator

What is Voltage Drop Calculator?

Voltage Drop Calculator helps you estimate resistive voltage drop along a cable from length and conductor area.

The main result is voltage drop, with a breakdown of percentage voltage drop. The formula, example and assumptions below explain how to interpret it.

How to use Voltage Drop Calculator

Use the example to get familiar with the form, then enter your own figures. Any rates in the example are illustrative. Check the field labels and units before calculating.

  1. Gather current (A), one-way cable length (m), conductor cross-section (mm²), conductor resistivity (Ω·mm²/m) and supply voltage (V). Use values from the same situation or reporting period.
  2. Replace the example current with your own value, then complete the other fields. Check the displayed units.
  3. Select Calculate and read voltage drop with its result breakdown. Change one input and calculate again to compare a second scenario. Reset restores the original example.
  • Enter current in A, at least 0. Decimals are accepted.
  • Enter one-way cable length in m, at least 0. Decimals are accepted.
  • Enter conductor cross-section in mm², at least 0.000001. Decimals are accepted.
  • Enter conductor resistivity in Ω·mm²/m, at least 0.000001. Decimals are accepted.
  • Enter supply voltage in V, at least 0.000001. Decimals are accepted.

Voltage Drop Calculator: a worked example

With the inputs below, the result is 5.25 V (voltage drop). Follow the example, then replace these illustrative values with your own.

Example inputs and output
Input or outputExample value
Current (A)20 A
One-way cable length (m)30 m
Conductor cross-section (mm²)4 mm²
Conductor resistivity (Ω·mm²/m)0.0175 Ω·mm²/m
Supply voltage (V)230 V
Voltage drop5.25 V
Percentage voltage drop2.282609 %

Understanding the Voltage Drop result

Read voltage drop alongside percentage voltage drop. These describe different parts of the same calculation.

Displayed results use a readable number of decimal places. When checking a result by hand, keep extra precision until the last step. To compare scenarios, change one input at a time and keep the others fixed.

  • Example Percentage voltage drop: 2.282609 %

Voltage Drop Calculator: assumptions and common mistakes

A useful estimate starts with the right inputs. Check the following assumptions and limits before applying the result to your situation.

  • DC, single-phase and three-phase calculations use different relationships. Equipment selection also depends on installation conditions and applicable standards.

For wider guidance, visit Bureau of Indian Standards. The formula and scope of this specific tool are stated on this page.

Voltage Drop Calculator FAQs

What does Voltage Drop Calculator calculate?

Voltage Drop Calculator helps you estimate resistive voltage drop along a cable from length and conductor area. Its main output is voltage drop in V.

What inputs do I need for Voltage Drop Calculator?

You need current (A), one-way cable length (m), conductor cross-section (mm²), conductor resistivity (Ω·mm²/m) and supply voltage (V). Use the field labels and units to match your figures to the formula.

Which formula does Voltage Drop Calculator use?

Two-wire DC / single-phase resistive approximation: voltage drop = 2 × resistivity × one-way length × current ÷ area. Reactance and temperature effects are not modelled.

What is a worked example for Voltage Drop Calculator?

Example inputs: Current: 20 A; One-way cable length: 30 m; Conductor cross-section: 4 mm²; Conductor resistivity: 0.0175 Ω·mm²/m. Keep the remaining inputs as shown in the worked-example table. The result is 5.25 V (voltage drop).

How should I enter current?

Enter current in A, at least 0. Decimals are accepted.

How do I choose one-way cable length?

Enter one-way cable length in m, at least 0. Decimals are accepted. The example uses 30 m; replace it if your circumstances differ.

How should I read voltage drop?

Read voltage drop alongside percentage voltage drop. These describe different parts of the same calculation.

Why might my Voltage Drop Calculator result differ from my records?

DC, single-phase and three-phase calculations use different relationships. Equipment selection also depends on installation conditions and applicable standards. Differences in entered values, units or rounding can also change the comparison.

Can I compare two scenarios in Voltage Drop Calculator?

Yes. Note your first voltage drop, change current or another input, and select Calculate again. Editing a field clears the old result so it is not mistaken for a new calculation.

Is Voltage Drop Calculator free, and where are my inputs calculated?

This calculator is free to use without signing in. Its formula runs in your browser; calculator inputs are not sent to a calculation API. The inputs reset to the example values when you reset the form or start a fresh page.