Wire Size Calculator (IEC mm² / NEC AWG) | Ampacity & Voltage Drop
Wire Size Calculator (IEC mm² / NEC AWG)
Wire Size Calculation Explained
This Wire Size Calculator recommends a conductor size based on two checks: ampacity (current-carrying capacity with derating) and voltage drop. Choose IEC (mm²) for Europe or NEC (AWG/kcmil) for the USA.
Rule of thumb: Pick the smallest size that passes ampacity, then increase if needed to meet voltage drop.
This selection changes ampacity tables, derating rules, and output units.
Use Power mode if you prefer entering kW + voltage + PF to calculate current.
Used to select conservative base ampacity.
Used for voltage drop estimation.
This tool provides a preliminary recommendation using simplified tables and assumptions. Final sizing must be verified against the applicable local code, installation conditions, and manufacturer data.
Show assumptions used
- Base ampacity tables are simplified and conservative.
- Temperature and grouping derating are approximate.
- Voltage drop uses resistive approximation (R) based on conductor area and material.
How Does the Wire Size Calculator Work?
Wire sizing is typically governed by two constraints: ampacity (the maximum current a conductor can safely carry under installation conditions), and voltage drop (the percentage of voltage lost along the cable run). This calculator recommends the smallest conductor size that passes both checks for the selected IEC (mm²) or NEC (AWG/kcmil) design basis.
1) Ampacity check (with derating)
The tool starts from a conservative base ampacity table and then applies approximate derating for: ambient temperature, installation method, and grouping (bundling). The recommended size must satisfy: Derated Ampacity ≥ Design Current.
2) Voltage drop check
The tool estimates voltage drop using conductor resistance derived from material and cross-sectional area. If the selected size exceeds your max voltage drop (%), the calculator increases the conductor size until the voltage drop target is met.
IEC vs NEC outputs
- IEC: Results shown in mm² with AWG/kcmil as an approximate equivalent.
- NEC: Results shown in AWG/kcmil with mm² as an approximate equivalent.
Because cable selection is code- and installation-dependent, treat results as a fast engineering estimate and confirm with the applicable standard and manufacturer documentation.
Wire Size Calculator FAQ
Is AWG the same as mm²?
Not exactly. AWG is a gauge system used mainly in North America, while mm² is a metric area. This tool shows an approximate equivalent, typically using the nearest standard size or the next size up.
Why does temperature and grouping change the recommended size?
Higher ambient temperatures and grouped conductors reduce heat dissipation, effectively lowering allowable current. Derating ensures the conductor remains within a safe operating temperature range.
Which is more important: ampacity or voltage drop?
Both matter. Ampacity protects against overheating, while voltage drop protects performance (especially for motors and sensitive loads). The recommended size should satisfy both constraints.