Wire Gauge Calculator
Find the right wire size for any electrical circuit — current capacity, resistance, and voltage drop.
📖 What is a Wire Gauge Calculator?
A wire gauge calculator helps electricians, engineers, and DIY enthusiasts select the correct wire size for any electrical circuit. Choosing the right wire gauge is critical for safety and efficiency — undersized wire overheats and is a fire risk, while oversized wire wastes money without adding benefit.
In the US and many other countries, wire size is measured in AWG (American Wire Gauge). The AWG system works inversely — a smaller number means a thicker wire. AWG 10 is thicker than AWG 14. For very large conductors, the kcmil (thousand circular mils) system is used instead.
This calculator provides two modes. The AWG Lookup mode gives you the diameter, cross-sectional area, resistance per metre, and maximum current capacity (ampacity) for any gauge of copper or aluminium wire. The Voltage Drop mode calculates how much voltage is lost along a given run of wire — essential for long cable runs in homes, solar installations, and industrial settings.
Wire ampacity depends on the insulation type, installation method (in conduit, buried, open air), ambient temperature, and bundling with other conductors. The values shown here are for single-conductor copper wire at 30°C ambient — always verify with NEC Table 310.16 or your local wiring regulations for final design.
📝 Wire Gauge Formulas
d = 0.005 × 92^((36 − AWG) / 39) inches
Cross-Sectional Area:
A = π × (d/2)² mm²
Resistance per metre (copper):
R/m = ρ / A where ρ(Cu) = 1.724 × 10⁻⁸ Ω·m, ρ(Al) = 2.82 × 10⁻⁸ Ω·m
Total Resistance (round trip):
Rtotal = R/m × 2 × L
Voltage Drop:
Vdrop = I × Rtotal
Voltage Drop Percentage:
Vdrop% = (Vdrop / Vsource) × 100
Where: d = diameter | A = area (m²) | ρ = resistivity | L = one-way length (m) | I = current (A)
✍️ How to Use This Calculator
- AWG Lookup mode: Select a wire gauge from the dropdown and choose copper or aluminium. Click Calculate to see diameter, area, resistance, and ampacity.
- Voltage Drop mode: Switch to the Voltage Drop tab, enter the wire gauge, current load, one-way run length, and system voltage.
- Click Calculate to see total resistance, voltage drop in volts, and voltage drop percentage.
- If voltage drop exceeds 3%, go up one or two AWG sizes (lower number) and recalculate.
- For critical runs, keep total drop (feeder + branch) below 5% per NEC recommendations.
📄 Example Calculations
A 20 A circuit needs wire with ampacity ≥ 25 A (125% rule for continuous loads).
AWG 12 copper has ampacity of 20 A (in conduit, 75°C). AWG 10 copper has ampacity of 30 A.
Result: Use AWG 10 copper for a 20 A continuous load (or AWG 12 if truly non-continuous).
Example 2 — Voltage drop for a 30 m run:
Circuit: 15 A load, AWG 12 copper, 30 m one-way run, 230 V system.
R/m (AWG 12 Cu) ≈ 0.00529 Ω/m
Rtotal = 0.00529 × 2 × 30 = 0.318 Ω
Vdrop = 15 × 0.318 = 4.76 V
Vdrop% = 4.76 / 230 × 100 = 2.07% ✓ (under 3%)