Cable Dimension Calculator (Voltage Drop Method)
Use this calculator to estimate cable cross-sectional area in mm² based on load current, cable length, acceptable voltage drop, and conductor material.
Why a cable dimension calculator matters
A cable dimension calculator helps you choose the correct conductor cross-sectional area so your installation runs safely and efficiently. If the cable is undersized, it can overheat, waste power, and create excessive voltage drop at the load. If it is oversized, your project may become unnecessarily expensive.
In practical terms, cable sizing is a balance between electrical performance, thermal limits, installation method, and budget. This calculator gives you a fast first-pass estimate using the voltage-drop method and a simple current-density check.
What this calculator uses
1) Voltage drop model
The main calculation determines the minimum area needed to keep voltage drop under your chosen limit.
- Single-phase AC and DC (2-wire): factor of 2
- Three-phase AC: factor of √3
- Material resistivity: copper or aluminum
- Temperature correction from 20°C using a linear coefficient
2) Simple ampacity sanity check
A rough current-density rule is also applied (6 A/mm² for copper, 4 A/mm² for aluminum) to avoid obviously small results. Final required area is the larger of:
- Area from voltage drop
- Area from current-density check
Important notes before you build
This tool is for preliminary design and quick comparisons. Real cable selection must consider standards and site conditions such as:
- Insulation type and allowable conductor temperature
- Cable grouping and installation method (tray, conduit, buried, free air)
- Ambient temperature correction factors
- Short-circuit withstand requirements
- Local electrical code requirements
- Protective device coordination
Typical voltage drop targets
Different projects use different design margins, but common targets include:
- Lighting circuits: 2% to 3%
- General power circuits: 3% to 5%
- Sensitive electronics: usually lower values for stability
If your run is very long, you may need to increase cable size significantly even at moderate current.
Example workflow
Step-by-step
- Choose system type (single-phase, three-phase, or DC).
- Enter current, one-way distance, and nominal voltage.
- Set the maximum voltage drop percentage (for example, 3%).
- Select conductor material and expected conductor temperature.
- Run calculation and choose the next standard cable size shown.
After that, verify ampacity and code compliance in the applicable design standard before procurement or installation.
Frequently asked questions
Is bigger cable always better?
Electrically, bigger cable generally means less voltage drop and lower losses. Economically, there is a point where extra copper or aluminum cost no longer provides enough benefit.
Why does aluminum often need a larger size?
Aluminum has higher resistivity than copper, so it needs more cross-sectional area to achieve similar voltage drop performance.
Can I use this for motor feeders?
You can use it as a starting point, but motors need additional checks: starting current effects, protection settings, and often stricter design assumptions.