Estimate solar DC cable size from current, one-way run length, voltage, drop limit, copper or aluminum material, and ampacity derating for rooftop, conduit, combiner, controller, battery, or inverter runs.
Area (mm²) = (2 × L × I × ρ) / ΔVSolar DC cable sizing normally starts with voltage drop. The direct formula uses one-way length, current, conductor resistivity, and allowed voltage drop to estimate the minimum cross-sectional area in mm². The calculator then rounds up to the first built-in AWG/mm² size that also passes the simplified derated ampacity check.
| Symbol | Variable | Description |
|---|---|---|
| 2 × L | Round-trip length | The one-way cable distance doubled for the positive and negative conductors. |
| I | Design current | Use the current the cable must safely carry. PV string work commonly uses a design current based on Isc rather than only Imp. |
| ρ | Conductor resistivity | Approximately 0.0175 Ω·mm²/m for copper and 0.0282 Ω·mm²/m for aluminum. |
| ΔV | Allowed voltage drop | System voltage multiplied by the selected drop percentage. |
Pick the circuit segment
Choose PV string, combiner/controller main, battery-to-inverter, or DC load branch so the result can be interpreted in the right context.
Enter design current
Use the current that the cable must carry. For PV strings, design current is often based on short-circuit current and code multipliers, not just operating current.
Measure one-way distance
Enter the physical one-way run. The calculator doubles it internally for DC round-trip voltage drop.
Set voltage, drop target, and material
Enter 12 V, 24 V, 48 V, or PV string voltage, choose copper or aluminum, and select a voltage-drop target such as 1%, 1.5%, 2%, 3%, or 5%.
Apply derating
Use temperature and grouping/conduit derating factors when cables are hot, bundled, in conduit, buried, or on rooftops.
Review both checks
Use a size that passes both voltage drop and derated ampacity. If the formula area exceeds the selected cable table, consider larger or parallel conductors with proper design review.
A solar cable should be large enough for both voltage drop and current carrying capacity. This calculator first estimates the formula-required cross-section in mm², then rounds up to an AWG/mm² table size that also passes the simplified derated ampacity check.
Design targets vary by system, standard, and project economics. Lower voltage drop costs more in copper or aluminum but reduces power loss.
| Target | Typical use | Tradeoff |
|---|---|---|
| 1% | PV string or critical low-voltage run | Larger cable, very low loss |
| 1.5% | DC main segment planning target | Common professional design budget |
| 2-3% | General solar charging or inverter cable planning | Balanced cost and efficiency |
| 5% | Less sensitive DC loads | Smaller cable, higher power loss |
Voltage drop and simplified ampacity are not enough for final procurement. Confirm conductor insulation, PV wire rating, UV and wet-location rating, temperature correction, conduit fill, terminal temperature limits, overcurrent protection, fault current, and whether parallel strings are fused.
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