24V Wire Size Calculator

Calculates the minimum copper or aluminum wire gauge (AWG) for a 24V DC circuit using the standard voltage-drop method, then reports the actual drop and power loss at that gauge.

Quick Facts

Formula
Area (CM) = 2 × K × L × I ÷ VD
K = 10.75 (copper) or 17.0 (aluminum), circular-mil-ohms per foot; L is one-way length, doubled for the return path.
Design target
3% max drop is a common target for lighting and electronics
Up to 5% is sometimes accepted for less sensitive loads.

Your Results

Calculated
Recommended wire gauge
-
Minimum AWG for this run
Minimum wire area
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Circular mils required
Actual voltage drop
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At the recommended gauge
Power loss in wire
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Heat dissipated at that gauge

Ready

Enter your current, length, voltage, and allowed drop, then press Calculate.

How 24V Wire Sizing Works

Every wire has resistance, and pushing current through that resistance over distance causes the voltage to drop between the source and the load. Undersized wire on a 24V circuit wastes power as heat and can starve lights, pumps, or electronics of the voltage they need to run correctly. This calculator applies the standard voltage-drop sizing method used for low-voltage DC runs — solar, marine, RV, automotive, and landscape lighting circuits — to find the smallest standard wire gauge that keeps the drop under your chosen limit.

The formula

The required conductor area in circular mils (CM) is:

CM = (2 × K × L × I) ÷ VD

  • K is the resistivity constant of the conductor in circular-mil-ohms per foot: 10.75 for copper, 17.0 for aluminum.
  • L is the one-way wire run in feet.
  • I is the load current in amps.
  • VD is the maximum voltage drop you're willing to allow, in volts (your percentage input times the system voltage).

The factor of 2 accounts for the round trip: current flows out to the load on one conductor and returns on another (or through a shared negative/ground), so the electrical path is twice the one-way distance you measure. Once the required area is known, it is converted to the smallest standard AWG gauge whose cross-sectional area meets or exceeds it — using the standard AWG diameter relationship where each step of 1 gauge number changes the diameter by a factor of 92^(1/39). The calculator then reports the actual drop and power loss (P = I × Vdrop) you'll see at that gauge, which will be at or under your allowed limit.

Reading the assumptions

  • K = 10.75 (copper) and K = 17.0 (aluminum) are standard circular-mil-ohms-per-foot constants for DC resistivity; actual resistance shifts slightly with temperature and stranding.
  • The 2× factor assumes a simple two-conductor loop (source and return); circuits that share a chassis or vehicle ground as the return path still use the same round-trip length.
  • Results recommend the smallest gauge that satisfies your inputs — going one or more sizes larger is always safe and further reduces drop and heat.

Frequently Asked Questions

What formula does this 24V wire size calculator use?
It uses the standard voltage-drop sizing formula: required area in circular mils = (2 x K x L x I) / VD, where K is a resistivity constant (10.75 for copper, 17.0 for aluminum, in circular-mil-ohms per foot), L is the one-way wire length in feet, I is the current in amps, and VD is the allowed voltage drop in volts. The result is converted to the nearest standard AWG gauge that meets or exceeds the required area.
Why is the wire length multiplied by two?
A DC circuit is a loop: current flows out to the load on one conductor and back on another (or through a shared ground/negative return). The 2x factor converts the one-way run you measure into the full round-trip length of conductor the current actually passes through, which is what determines total resistance and voltage drop.
What voltage drop percentage should I use for a 24V system?
A common design target is 3% or less for lighting and sensitive electronics, with up to 5% sometimes accepted for less sensitive loads like heaters or motors. Larger drops waste power as heat and can cause dim lights or erratic behavior in electronics. This calculator lets you set any allowed percentage so you can compare gauges at different targets.
Should I size for copper or aluminum wire?
Copper has lower resistance than aluminum, so a copper conductor can be smaller for the same current, length, and voltage drop. This calculator uses K = 10.75 for copper and K = 17.0 for aluminum (circular-mil-ohms per foot); switching the material option recalculates the required gauge for that conductor's resistivity.

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