Free Cable Thickness Calculator (mm² & AWG)
Estimate the minimum cable size required to keep voltage drop within your target limit. This tool supports copper and aluminum conductors for DC, single-phase AC, and three-phase AC circuits.
What this cable thickness calculator does
This calculator estimates cable cross-sectional area (in mm²) needed to satisfy a voltage drop limit. In practical wiring design, cable size is not only about carrying current safely; it is also about delivering enough voltage at the load. If the cable is too thin, voltage drop increases, equipment performance suffers, and losses rise.
The tool gives you:
- Theoretical minimum conductor area based on voltage drop formula
- Nearest standard cable size
- Ampacity-aware recommendation (using conservative reference values)
- Approximate AWG equivalent for quick comparison
How the calculation works
1) Set allowable voltage drop
Allowed voltage drop is calculated from your percentage input:
ΔVallowed = V × (drop% / 100)
2) Compute minimum area from conductor resistance
Using resistivity values at about 20°C, the calculator solves for cable area:
- DC / single-phase: A = (2 × ρ × I × L) / ΔV
- Three-phase: A = (√3 × ρ × I × L) / ΔV
Where A is area (mm²), ρ is resistivity (Ω·mm²/m), I is current (A), and L is one-way length (m).
3) Select a standard size and check ampacity
The computed area may not exactly match market cable sizes, so the calculator rounds up to the next standard size. Then it checks a conservative ampacity table. If needed, it moves up again to avoid undersizing for current carrying capacity.
When to use this tool
- Solar DC runs between charge controller and battery bank
- Single-phase feeders for homes, workshops, and subpanels
- Three-phase motor or distribution cables
- Preliminary design and budgeting before final engineering review
Important design factors beyond this calculator
Ambient temperature and grouping
Hot environments and tightly bundled cables reduce current capacity. Real installations often require derating factors that are not included in this simplified calculator.
Installation method
Cable in conduit, buried cable, tray cable, and free-air cable all behave differently thermally. Ampacity can vary significantly for the same conductor size.
Insulation and terminal limits
Insulation type (PVC, XLPE, etc.) and terminal temperature ratings can constrain permissible current.
Local code compliance
Always verify with applicable standards and electrical code requirements in your jurisdiction (for example NEC, IEC, BS, AS/NZS, or local utility rules).
Quick cable sizing tips
- For long runs, voltage drop usually drives cable size more than ampacity.
- Using higher system voltage can reduce required cable thickness.
- Copper needs less area than aluminum for the same drop target.
- Motors and sensitive electronics often perform better with tighter drop limits.
Frequently asked questions
Is cable thickness the same as diameter?
Not exactly. Electrical sizing normally uses cross-sectional area (mm²), while physical thickness can refer to outside diameter including insulation.
What voltage drop percentage should I choose?
Common targets are 2% to 5%, depending on application. Critical loads may use tighter limits; general circuits may allow higher values where code permits.
Can I use this for final stamped designs?
Use it for fast estimates. Final designs should include full derating, fault level checks, protective device coordination, and code-based conductor selection by a qualified professional.