Cable & Inverter Sizing Calculator

Undersized DC cable in a 12V/24V system wastes power as heat and voltage drop before it ever reaches the load — the standard fix (used across marine and van DC wiring guides) is to size the cable to a maximum acceptable voltage drop, not just to "looks about right".

• Current (A) = power (W) ÷ system voltage (V).
• Cross-section (mm²) = (2 × cable length (m) × current (A) × copper resistivity) ÷ allowed voltage drop (V). Copper resistivity ≈ 0.0175 Ω·mm²/m at 20°C — a standard physical constant, not an assumption; the factor of 2 accounts for the outbound + return conductor.
• The calculated section is rounded UP to the next standard cable size, then matched to its nearest AWG equivalent using a published metric↔AWG conversion table — this equivalence is approximate by nature (metric and AWG sizes never align exactly); confirm against your chosen cable's datasheet.
• Fuse/breaker rating is rounded up to the next standard size above 125% of the continuous current — standard practice for protecting continuously-loaded cable (the ABYC E-11 / NEC 240.4(D) approach: the fuse protects the CABLE, not just the appliance).
• Inverter continuous rating recommended at 125% of the continuous load (a common manufacturer sizing margin); peak/surge rating shown at 2× continuous — a rule of thumb for motor/compressor start-up current, attributed here, not a spec for any specific appliance. Check the actual inrush current of your heaviest load (compressor fridge, motor, etc.).