24V Wire Size Calculator - DC and Single-Phase Conductor Size

A 24V wire size calculator turns four measurements - allowable voltage drop, load current, one-way cable run, and conductor material - into the minimum cross-sectional area a 24V DC cable needs at the load. The result comes back in mm^2 for metric labels and AWG for North American projects.

• • Trolling Motor and Marine Runs: Sizing the battery-to-motor cable on a 24V trolling motor where voltage drop steals thrust at the prop.
• • Off-Grid Solar Arrays: Sizing the PV-to-controller and battery-to-inverter runs on a 24V solar system where 2 percent drop protects inverter efficiency.
• • 24V LED Strip and Sign Feeders: Sizing long 24V LED runs so the far end of the strip keeps its rated brightness instead of dimming yellow.

Wire sizing for a 24V circuit is a two-part problem: the cable has to carry the load current without overheating and deliver enough voltage at the far end. A 3 percent drop is only 0.72 V on 24V but 6.6 V on 220V, so a thin cable can starve a 24V LED strip within metres.

When the same load runs on a 220V source instead, the 220V wire size calculator applies the same voltage-drop formula to the household single-phase supply so the cross-section and AWG answer lines up across both voltages.

The 24V wire size formula divides the allowed voltage drop by the conductor resistivity, current, and run length. The factor of two accounts for both conductors in the DC loop, and three-phase systems use sqrt(3) in place of the two.

• Loop factor: 2 for DC or single-phase AC, sqrt(3) for three-phase AC.
• Voltage drop V: Allowed drop in volts; 0.72 V for 3 percent of 24V.
• Current I: Maximum continuous load current in amperes.
• Distance L: One-way cable length in metres, doubled internally for the loop.
• Resistivity rho: Copper 1.68 x 10^-8 ohm-m at 20 C, aluminum 2.82 x 10^-8 ohm-m at 20 C.

The mm^2 result converts to AWG by rounding up to the next standard gauge. That round-up keeps the cable inside the voltage-drop target, because real cables are slightly smaller than the geometric ideal. For source voltages above 50 V with one-way distances under 16 m, the calculator clamps the effective distance to 16 m so a short run does not produce a cable too thin for a longer run.

According to Omni Calculator, 24V Wire Size, the formula for a DC or single-phase 24V system is A = (2 x I x rho x L) / V and the three-phase formula replaces the 2 with sqrt(3) and returns the area of a single conductor.

When the recommended cable needs a sanity check against the basic V = I x R relationship, the Ohm's Law calculator shows how the same current, voltage, and resistance values line up against the cross-section the formula recommends.

Four small concepts explain what the cross-section number means on a 24V system, where voltage drop is amplified by the low source voltage.

The cross-section in mm^2 ties together resistance, ampacity, and voltage drop. Once you know the mm^2, the cable reel and the fuse rating line up against the same number.

When the chosen cable also has to satisfy ampacity and conduit fill alongside voltage drop, the wire gauge calculator produces the matching AWG size from load, distance, and a 12V, 24V, or solar-panel context, so the 24V result can be paired with the right cable for each part of the installation.

Six short steps take you from a 24V battery or solar source to a cross-section and AWG size that lines up with the fuse you plan to fit.

1. 1 Pick the System Type: Choose DC / AC single-phase for battery, solar, LED, and trolling motor runs. Pick three-phase for industrial 24V motor feeds.
2. 2 Set the Allowed Voltage Drop: Type the absolute voltage drop. For 3 percent of 24V enter 0.72 V; for 2 percent enter 0.48 V; for 5 percent enter 1.20 V.
3. 3 Enter the Load Current: Take the maximum continuous current from the equipment nameplate. Inrush current does not set the cable size on a DC feeder.
4. 4 Measure the One-Way Run: Measure the cable route from the battery or supply to the load. The calculator doubles the one-way distance internally for the DC loop.
5. 5 Choose the Conductor Material: Pick copper for most indoor 24V runs. Pick aluminum for long, low-cost outdoor feeders.
6. 6 Set the Maximum Wire Temperature: Type the maximum temperature the conductor will see. Use 75 C for PVC, 90 C for THHN inside conduit, 105 C for engine bays.

Picture a 24V trolling motor drawing 30 A from a battery 6 m away. Type DC / single-phase, 0.72 V, 30 A, 6 m, copper, 75 C. The calculator returns about 10.20 mm^2, which rounds up to 7 AWG with a 3.60 mm diameter and a 0.72 V drop at the motor. 7 AWG pairs with a 40 A fuse.

When the next step is to verify the cable against a different percent target or a multi-segment run, the voltage drop calculator handles the same math with explicit input fields so the 24V result can be cross-checked against a different cable layout.

A small dedicated 24V wire size calculator saves time on the math and produces a result that lines up with the cable reel and the fuse block.

• • Stops the Low-Voltage Guesswork: Replaces the percent-times-current-times-resistivity division with a single typed entry, so 3 percent on 24V stops being a manual 0.72 V multiplication.
• • Speaks mm^2 and AWG at the Same Time: Returns the cross-section in mm^2 for the metric reel and in AWG for the North American project.
• • Covers Copper and Aluminum: Lets the user pick the conductor material so the resistivity matches the cable, including the temperature rise from 1.68 to 2.11 x 10^-8 ohm-metres at 75 C.
• • Configurable Voltage Drop Target: Accepts any allowed drop in volts from 0.01 to 50, so the same calculator handles 2 percent for solar and 5 percent for battery feeds.
• • Shows the Diameter for Lug Sizing: Returns the conductor diameter in mm and inches, which is what you need to pick the right battery lug.

The biggest practical benefit on 24V systems is that the calculator does the doubling and the percent-to-volts conversion internally. Typing the loop length or the percent value directly is the two most common mistakes on a 24V install.

When the project also has to plan the total panel or battery load before sizing any individual branch, the electrical load calculator adds up the running and starting amps across the whole 24V system so the cable fits inside the supply rating.

Five physical and code factors shift the recommended mm^2 and AWG up or down from the textbook number.

• • The formula assumes a DC or single-phase loop with the same cable in both conductors and ignores the small resistance added by terminations, fuses, and splices.
• • Voltage-drop sizing is a sizing minimum. The recommended mm^2 also has to satisfy the ampacity tables and be protected by a fuse or breaker rated for the cable.

Practical installations also depend on the cable insulation. MTW, THHN, and marine-grade battery cable have different ampacity ratings at the same AWG, so the same mm^2 will deliver different currents in different cable types. On long 24V solar runs the temperature term matters most because combiner boxes reach 60-70 C in summer sun.

According to Wikipedia, Electrical resistivity and conductivity, copper has 1.68 x 10^-8 and aluminum 2.82 x 10^-8 ohm-metres at 20 C with a copper temperature coefficient of 0.00393 per C that drives the 75 C copper value of about 2.11 x 10^-8 ohm-metres used in 24V wiring tables.

According to Wikipedia, American wire gauge, the AWG system is a 39-step geometric progression from 36 AWG to 0000 AWG with a 92x diameter ratio that defines the mm^2 per AWG table used to round up the calculated cross-section.

When the cable is sized and the next step is the fuse or breaker rating, the circuit breaker size calculator picks the correct overcurrent protection for continuous and motor loads so the AWG from this calculator lines up with the fuse block in the panel.