DC Voltage Drop Calculator
Estimate wire voltage drop for low-voltage DC systems (solar, RV, marine, automotive, battery banks, and control circuits).
What is DC voltage drop?
DC voltage drop is the amount of voltage lost as current moves through a wire. Every conductor has resistance, so a longer run, higher current, or smaller wire creates more drop. In practical terms, the device at the far end receives less voltage than your source provides.
This matters most in low-voltage systems like 12V and 24V battery setups, because even a small absolute drop can be a large percentage of total system voltage.
Formula used in this calculator
Voltage Drop (V) = Current (A) × Total Circuit Resistance (Ω)
Total Circuit Resistance (Ω) = (Wire resistance per 1000 ft ÷ 1000) × Length (ft) × Path factor
- Path factor = 2 for typical positive-and-negative two-wire DC circuits.
- Path factor = 1 when using a chassis return or equivalent single-conductor return model.
- Aluminum is modeled with higher resistance than copper.
How to use the calculator
1) Enter electrical load values
Input your source voltage and expected current draw at full load. Use realistic current values, not just idle values.
2) Enter wire run details
Use one-way distance from source to load. Then choose whether your return path effectively doubles the circuit length.
3) Select material and AWG size
Pick copper or aluminum and the wire gauge you plan to install. The calculator uses standard resistance approximations to estimate losses.
4) Review the result
You will see:
- Total circuit resistance
- Voltage drop in volts
- Voltage drop percentage
- Estimated voltage delivered to the load
- Power dissipated in the cable
- A suggested wire size to meet your target drop
What is an acceptable voltage drop?
- Up to 3%: commonly recommended for sensitive loads and branch circuits.
- 3% to 5%: often acceptable for non-critical loads, depending on equipment tolerance.
- Above 5%: usually a sign to increase wire size, reduce length, or reduce current.
Always verify against your local electrical code and the manufacturer’s minimum voltage requirements.
Practical tips to reduce DC voltage drop
- Use a larger conductor (lower AWG number or larger 1/0, 2/0, etc.).
- Shorten cable length where possible.
- Move power electronics closer to the load.
- Use higher system voltage (for the same power, current drops).
- Check all terminals and connections for heat, corrosion, and loose crimps.
Example scenario
Suppose a 12V system powers a 20A load located 25 ft away (one-way), using a two-conductor circuit. If wire resistance is too high, the load may receive under 11V during operation, causing dim lights, motor slowdown, or inverter low-voltage alarms. Increasing wire size sharply reduces loss and improves reliability.
FAQ
Does this include temperature correction?
No. Real conductor resistance increases with temperature. For hot environments or bundled conductors, design conservatively and verify with code tables.
Can I use this for AC circuits?
This tool is intended for DC voltage drop. AC calculations can involve additional factors such as reactance and power factor.
Is AWG the only sizing system?
This page uses AWG because it is common in North America. If you size in mm², convert to an equivalent conductor resistance and verify with your standard tables.
Engineering note: This calculator is a planning aid. Always confirm final design using applicable code requirements, installation conditions, and manufacturer specifications.