Wire Size Calculator for DC Circuits – mm², AWG & Voltage Drop
Looking for a reliable wire size calculator for your DC project?
This free wire size calculator helps you determine the minimum required cable thickness in mm², based on wire length, voltage drop, current, and power. It supports both copper and aluminum conductors, and also offers optional conversions to AWG and SWG.
Designed specifically for DC circuits — such as solar panel systems, battery-powered devices, LED lighting, and e-bike wiring — this tool ensures your cables are sized correctly for both safety and performance.
After calculation, always round up to the next thicker standard size available in stores or suppliers. That way, your system stays efficient and within safe electrical limits.
No sign-up, no complexity — just quick, accurate results in seconds.
New to DC wiring? Start with our in-depth DC Cable Sizing Guide to understand the principles before calculating. Understanding voltage drop is essential when working with DC wiring. It affects the performance and safety of your electrical system, especially over longer distances. Learn more about voltage drop and how it impacts circuit efficiency. Or just head straight to our tool.
How to Use the DC Wire Size Calculator
Why use this wire size calculator?
- Calculates wire thickness based on voltage drop, length, and current/power
- Supports both copper and aluminum wire types
- Output in mm², with optional AWG and SWG equivalents
- Ideal for DC systems: solar panels, batteries, LED setups, and e-bikes
- Ensures safe wire sizing by calculating the minimum cross-section
- Always advises to round up to the next standard size available
- Fully browser-based — no login or installation required
- Calculate the minimum wire size in mm² for your electrical project. Enter the wire length, acceptable voltage drop, and at least two of power, voltage, or current. Optionally convert results to AWG or SWG.
Frequently Asked Questions (FAQ)
What does this wire size calculator actually calculate?
This calculator determines the minimum required wire cross-sectional area in square millimeters (mm²), based on wire length, voltage drop, and either power, voltage, or current. It also provides optional conversions to AWG (American Wire Gauge) and SWG (Standard Wire Gauge).
Can I use this calculator for AC (alternating current) circuits?
No. This tool is intended for DC circuits or systems where the current flows in both directions through the same wire. For household or industrial AC wiring, always follow national electrical codes and consult a licensed electrician.
How do I use the calculator if I only know voltage and power?
Simply enter the voltage (V) and power (W). The calculator will automatically calculate the current (I = P ÷ V) and proceed with the wire sizing. Not sure how to measure voltage or current? Check out our guide: How to Use a Multimeter for Beginners
What does “minimum wire size” mean?
The result from the calculator represents the absolute minimum wire size required to meet your selected voltage drop. In practice, always round up to the next standard wire size available to ensure safe and compliant installations.
What is the difference between mm², AWG, and SWG?
- mm² is the metric measurement of a wire’s cross-sectional area.
- AWG is a North American standard based on wire diameter.
- SWG is a British standard also based on diameter.This calculator provides all three formats for convenience and international compatibility.
Is this tool suitable for e-bike wiring?
Yes. This calculator is well-suited for e-bikes, electric scooters, and other battery-powered applications where accurate wire sizing and voltage drop control are important.
Does voltage drop really matter?
Yes. Excessive voltage drop can lead to power loss, overheating, reduced device performance, and safety hazards. Correct wire sizing ensures efficient energy delivery and long-term system reliability, especially in low-voltage or long-distance setups.