Cable Size Calculator
This cable size calculator helps you select the correct electrical cable sizing (IEC) based on load current, system voltage, phase, and conductor material. Use this electrical calculator for wire sizing in industrial and commercial design.
For detailed guides and examples, see our Cable and Protection Guide
Input Parameters
Calculation Results
⚠️ Professional Disclaimer: This cable sizing is a simplified IEC-style recommendation based on current only. Final cable selection must consider installation method, grouping, ambient temperature, insulation type, voltage drop, short-circuit withstand, and applicable standards (IEC/NEC) verified by a qualified engineer.
Why this result? (Optional)
Calculation InsightsHow to Calculate Cable Size
Method: Select the next higher standard cable cross-section whose typical current rating is equal to or above the design load current.
This tool uses a simplified IEC-style table such as: 15 A → 1.5 mm², 20 A → 2.5 mm², 30 A → 4 mm², 40 A → 6 mm², 55 A → 10 mm², 75 A → 16 mm², 100 A → 25 mm², 125 A → 35 mm², 150 A → 50 mm², 200 A → 70 mm².
Use the result as an initial suggestion in feeder design, motor distribution, and panel outgoing selection. Always verify against detailed manufacturer tables including derating factors, voltage drop, and installation conditions.
Typical Examples
- Example 1: 25 A branch circuit in a small panel can start from 4 mm² preliminary cable selection.
- Example 2: 90 A feeder for a production line can require 25-35 mm² depending on installation derating.
- Example 3: 180 A distribution feeder may move to 70 mm² after ampacity and voltage drop checks.
Guides for Cable Selection
For full explanations and more advanced sizing, see:
Frequently Asked Questions
What is a cable size calculator used for?
It is used for preliminary cable cross-section estimation before detailed derating and voltage-drop verification.
How to calculate cable size for a given load?
Calculate load current first, then select the next higher standard cable size from ampacity tables and validate installation corrections.
What is the cable sizing method formula?
A practical method is to choose the smallest standard cable whose allowable current is above the design current after correction factors.
Can you provide a cable sizing example?
Example: for about 45 A design current, start with the next standard cable above that current and then check derating and voltage drop.
Does cable size depend only on current?
No. This tool uses current-only as a quick starting point. Real designs must also include voltage drop, installation method, ambient temperature, grouping, and fault current limits.
What is the difference between copper and aluminum cables?
Copper has higher conductivity, so it carries more current for the same cross-section and is more compact, but more expensive. Aluminum is lighter and cheaper but often requires a larger cross-section and special terminations.
How does voltage drop affect cable sizing?
Long runs at high current can cause significant voltage drop. In many standards you must keep voltage drop below a specified percentage, which may require a larger cable than indicated by current capacity alone.
Do I need to apply derating factors?
Yes, for grouped cables, high ambient temperature, or special installation methods (for example in tray, conduit, buried) derating factors from IEC/NEC tables must be applied. This tool assumes typical conditions.
Is this calculator suitable for final design?
No. It is intended for quick checks and concept design. Final cable selection must follow detailed tables from standards and manufacturers, and should be validated by a qualified electrical engineer.