Wire Gauge Calculator
Find the right wire size
Current and voltage drop
AWG chart
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You're wiring a 30A circuit. Is 10 AWG enough? The shed is 200 feet from the panel—how much voltage will you lose? The extension cord feels warm. Is it undersized?
Wire gauge determines how much current a conductor can safely carry. Too small and wires overheat, causing fire hazards. Too large and you're wasting money on copper. This calculator sizes wire correctly for your application.
What is Wire Gauge?
Wire gauge measures conductor diameter, with smaller numbers indicating thicker wire. In the American Wire Gauge (AWG) system, each step represents roughly 26% change in cross-sectional area, affecting current capacity and resistance.
Key relationships:
Lower AWG = Thicker wire = More current capacity = Less resistance
Common gauges:
14 AWG: 15A circuits, typical residential lighting
12 AWG: 20A circuits, residential outlets
10 AWG: 30A circuits, dryers, water heaters
8 AWG: 40A circuits, ranges, large appliances
6 AWG: 55A circuits, AC units, subpanels
Every 3 gauge numbers doubles the cross-sectional area. 11 AWG has twice the copper of 14 AWG.
Why People Actually Need This Tool
Wire carrying too much current overheats. Insulation degrades, potentially causing electrical fires. Code requirements exist for safety.
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New circuits — Size wire for load and breaker rating.
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Long runs — Calculate voltage drop over distance.
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Solar installations — Size DC wiring for efficiency.
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Automotive — Select wire for 12V high-current accessories.
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Extension cords — Verify cord is adequate for load.
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Subpanel feeds — Size wire for amperage and distance.
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Speaker wire — Balance cost and signal quality.
How to Use the Wire Gauge Calculator
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Enter current (amps) — The load your circuit will carry.
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Enter distance — One-way length (calculator doubles for round-trip).
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Enter acceptable voltage drop — Typically 3% max.
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Enter voltage — 120V, 240V, 12V DC, etc.
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Get recommended gauge — Plus voltage drop and power loss.
| AWG | Diameter (mm) | Max Amps (copper) | Resistance (Ω/1000ft) |
|---|---|---|---|
| 14 | 1.63 | 15A | 2.52 |
| 12 | 2.05 | 20A | 1.59 |
| 10 | 2.59 | 30A | 1.00 |
| 8 | 3.26 | 40A | 0.63 |
| 6 | 4.11 | 55A | 0.40 |
| 4 | 5.19 | 70A | 0.25 |
| 2 | 6.54 | 95A | 0.16 |
Bundled cables, conduit fill, and ambient temperature all reduce safe ampacity. NEC tables give derating factors.
Real-World Use Cases
1. The Dryer Circuit
Context: Installing 30A 240V dryer circuit. Run is 40 feet.
Problem: What wire gauge required?
Solution: 30A requires 10 AWG minimum. At 40 feet, voltage drop is 1.5%—acceptable.
Outcome: Code-compliant, safe installation.
2. The Long Shed Run
Context: 100A subpanel in shed, 200 feet from main panel.
Problem: Wire size for acceptable voltage drop?
Solution: 100A at 200ft in 240V needs 1 AWG for 3% drop. Upgrade to 1/0 for margin.
Outcome: Proper voltage at shed even under full load.
3. The Solar Array
Context: 30A at 48V DC, 50 feet from panels to charge controller.
Problem: Wire size for DC application?
Solution: 30A, 50ft, 48V, 2% drop max → Need 4 AWG. DC is more sensitive to voltage drop.
Outcome: Efficient power transfer from panels.
4. The Car Audio
Context: 1000W amplifier in car. 12V system, 15ft from battery.
Problem: What power wire gauge?
Solution: 1000W at 12V = 83A. 15ft, 3% drop → Need 2 AWG (really 1/0 for margin).
Outcome: Amplifier gets clean, full power.
5. The Extension Cord Check
Context: Running 1500W space heater on 100ft extension cord.
Problem: Is typical 14 AWG cord safe?
Solution: 1500W at 120V = 12.5A. 14 AWG at 100ft drops 5V (4.2%)—marginal. Cord will be warm.
Outcome: Use 12 AWG cord for long runs with high loads.
6. The Speaker Wire
Context: Running 50ft speaker wire to outdoor speakers. 8Ω impedance.
Problem: What gauge for minimal signal loss?
Solution: 50ft to 8Ω speakers: 16 AWG gives 0.5Ω resistance (6% of load)—acceptable.
Outcome: Full audio quality without expensive overkill.
7. The RV Hookup
Context: 30A RV pedestal, 75ft cord.
Problem: Will 10 AWG handle this distance?
Solution: 30A, 75ft, 120V: 10 AWG drops 5.6V (4.7%). Upgrade to 8 AWG for 3%.
Outcome: Full voltage at RV for AC and appliances.
Common Mistakes and How to Avoid Them
Electricity travels to the load AND back. A 50ft run is 100ft of wire total. Don't forget the return path.
Privacy and Data Handling
This Wire Gauge Calculator operates entirely in your browser.
- No calculations are sent to any server.
- No electrical plans are stored.
- No account required.
- Works completely offline.
Your projects stay private.
Conclusion
Proper wire sizing balances safety, performance, and cost. Undersized wire is dangerous. Oversized wire wastes money. The right gauge delivers full power safely over the required distance.
This calculator accounts for current, distance, and voltage to recommend the correct gauge. Don't guess—calculate.
The right wire makes the circuit work right.