What is Wire Size Calculator?
Wire Size Calculator helps you estimate conductor area from voltage-drop and current-density limits.
The main result is minimum estimated conductor area, with a breakdown of voltage-drop requirement and current-density requirement. The formula, example and assumptions below explain how to interpret it.
How to use Wire Size 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.
- Gather design current (A), one-way cable length (m), supply voltage (V), maximum voltage drop (%), conductor resistivity (Ω·mm²/m) and permitted current density (A/mm²). Use values from the same situation or reporting period.
- Replace the example design current with your own value, then complete the other fields. Check the displayed units.
- Select Calculate and read minimum estimated conductor area with its result breakdown. Change one input and calculate again to compare a second scenario. Reset restores the original example.
- Enter design current in A, at least 0. Decimals are accepted.
- Enter one-way cable length in m, at least 0. Decimals are accepted.
- Enter supply voltage in V, at least 0.000001. Decimals are accepted.
- Enter maximum voltage drop in %, at least 0 and at most 100. Decimals are accepted.
- Enter conductor resistivity in Ω·mm²/m, at least 0.000001. Decimals are accepted.
- Enter permitted current density in A/mm², at least 0.000001. Decimals are accepted.
Wire Size Calculator: a worked example
With the inputs below, the result is 5 mm² (minimum estimated conductor area). Follow the example, then replace these illustrative values with your own.
| Input or output | Example value |
|---|---|
| Design current (A) | 20 A |
| One-way cable length (m) | 30 m |
| Supply voltage (V) | 230 V |
| Maximum voltage drop (%) | 3 % |
| Conductor resistivity (Ω·mm²/m) | 0.0175 Ω·mm²/m |
| Permitted current density (A/mm²) | 4 A/mm² |
| Minimum estimated conductor area | 5 mm² |
| Voltage-drop requirement | 3.043478 mm² |
| Current-density requirement | 5 mm² |
Understanding the Wire Size result
Read minimum estimated conductor area alongside voltage-drop requirement and current-density requirement. 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 Voltage-drop requirement: 3.043478 mm²
- Example Current-density requirement: 5 mm²
Wire Size 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.
- Engineering estimate, not a cable-code selection. Installation method, insulation, temperature, fault protection and standard size rounding must be checked separately.
- 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.
