Voltage Drop Calculator (12V DC)
Use this 12v wire size calculator to estimate voltage drop, percentage loss, delivered voltage, and suggested cable gauge.
Why voltage drop matters in 12V DC systems
On a 12 volt DC setup, even a small wiring loss can have a big effect. A half-volt drop is only minor in a 120V AC circuit, but in a 12V circuit it is over 4% loss. That can make LED lights dim, pumps run weakly, and compressors or inverters shut down early.
Whether you are wiring an RV, marine battery bank, off-grid solar system, car audio amplifier, or low-voltage lighting run, checking DC cable voltage drop helps you choose the right wire gauge before installation.
How this 12 volt dc voltage drop calculator works
This calculator uses standard conductor resistance values (ohms per 1000 ft) and applies the basic DC voltage drop formula:
Circuit resistance includes both outgoing and return conductors, so total wire length is one-way length × 2.
Outputs include:
- Voltage drop in volts
- Percentage voltage drop
- Voltage available at the load
- Approximate wiring power loss (watts)
- Recommended AWG based on your target drop percentage
How to use the calculator
1) Enter electrical load and length
Type the expected current draw in amps, and the one-way cable distance from source to load. You can use feet or meters.
2) Select cable details
Choose the existing (or planned) AWG size and material. Copper is the default and generally gives lower resistance than aluminum.
3) Set a target drop
For many 12V circuits, 3% is a common design target. Critical electronics sometimes use 2% or less. Non-critical loads may tolerate more.
4) Click calculate
You will immediately see whether your selected wire is acceptable and what gauge is suggested to hit your desired voltage-drop limit.
Typical voltage drop guidance for 12V wiring
- 0% to 3% — Excellent for most 12V DC distribution.
- 3% to 5% — Usually acceptable for moderate loads.
- Above 5% — Often problematic; consider larger wire or shorter run.
| AWG | Copper Resistance (Ω / 1000 ft) | Common Use Case |
|---|---|---|
| 14 | 2.525 | Short lighting and accessory circuits |
| 12 | 1.588 | General 12V branch circuits |
| 10 | 0.999 | Medium-load runs, fridges, pumps |
| 8 | 0.628 | Higher current or longer cable runs |
| 6 | 0.395 | Inverters and heavy DC loads |
| 4 | 0.249 | Battery interconnects and large loads |
Real-world examples
LED lighting run
A 5A LED circuit at 20 ft one-way on 14 AWG copper drops roughly 0.50V (about 4.2%). Moving to 10 AWG reduces that to around 0.20V (about 1.7%).
RV compressor fridge
A 12A load over 15 ft one-way on 8 AWG gives around 0.23V drop (about 1.9%). That usually keeps startup and low-voltage cutout issues under control.
Common mistakes to avoid
- Using one-way length only in formulas (you must include return path).
- Sizing wire only by ampacity and ignoring voltage drop.
- Choosing aluminum cable without accounting for higher resistance.
- Assuming every 12V load can tolerate 10% drop (many cannot).
- Ignoring connector, fuse block, and terminal resistance.
FAQ
Is this also a 24V or 48V voltage drop calculator?
Yes. Enter any system voltage in the field. The math works for 12V, 24V, 36V, and 48V DC systems.
Why does long wire length hurt so much?
Resistance increases with conductor length. Double the run, and voltage drop roughly doubles at the same current and wire gauge.
Should I design for 3% or less?
For sensitive electronics, radios, control boards, and inverter inputs, 3% or less is a solid target. For mission-critical equipment, many designers go lower.
Note: This tool provides engineering estimates for planning. Final installations should follow local electrical code, manufacturer instructions, and safety standards.