Calculate Correct Electrical Cable Size by Amperage
Proper electrical cable sizing is essential for safe DIY home and construction projects. Undersized wire causes voltage drop and creates serious safety hazards. Our calculator helps you determine the correct wire gauge based on your amperage load and installation distance, following industry standards and best practices. All calculations are current for 2026.
When to use this calculator
- DIY home electrical projects and installation planning
- Professional electricians verifying cable sizing standards
- Students learning electrical theory and design principles
- Building code compliance and safety verification
- Quick reference for selecting correct cable gauge on job sites
Sample Calculation
- Example
- Result
How it works
1 min readHow to Calculate Electrical Cable Size
The correct wire gauge depends on two critical factors: the amperage (current) load and the distance the current must travel. Using an undersized cable causes voltage drop—a dangerous reduction in voltage that can damage equipment, reduce appliance efficiency, or even create fire hazards.
The Formula
This calculator uses industry-standard electrical formulas that follow NIST (National Institute of Standards and Technology) and NEC (National Electrical Code) guidelines. Simply enter your circuit's amperage requirement and the length of your wire run, and we'll calculate the minimum cable gauge needed to safely deliver power without excessive voltage drop.
Key Principles
Important Notes
This calculation provides a reference guide for educational and planning purposes. For critical electrical installations, licensed buildings, or applications requiring code compliance, always consult a licensed electrician and verify all calculations against local electrical codes and standards. Results are based on standard copper conductors at typical ambient temperatures.
Frequently asked questions
What size wire do I need for 30 amps at 100 feet?
For a 100-foot run at 30 amps, you typically need 8 AWG copper wire to keep voltage drop within safe limits. Use our calculator to determine the exact size for your specific amperage and distance.
How does distance affect the required wire size?
Longer cable runs require thicker wire to prevent voltage drop. The relationship is roughly proportional—doubling the distance typically requires the next gauge size up.
What is voltage drop and why does it matter?
Voltage drop is the loss of electrical pressure as current travels through a cable. Excessive voltage drop reduces appliance performance, increases heat, and creates fire hazards. This calculator helps you avoid it.
Can I use a thinner gauge wire to save money?
No. Undersized wire is a safety hazard. It causes dangerous overheating, voltage loss, and potential fires. Proper sizing is not optional—it's a building code requirement.
What's the difference between AWG and metric cable sizes?
AWG (American Wire Gauge) is the North American standard. Metric sizes are used internationally. This calculator supports both measurement systems.
How often are electrical standards updated?
The National Electrical Code (NEC) updates every three years. Our calculator data is current as of 2026 and reviewed regularly.
Is this calculator free to use?
Yes, completely free. No registration, sign-up, or fees required.
Do you store my calculations or personal data?
No. All calculations run directly in your browser. We never send your data to any server.
How accurate are these results?
Our calculations use industry-standard formulas validated internationally. Results are practical estimates within ±5-10% depending on specific materials and conditions. Always verify with a licensed electrician for critical installations.