6 AWG vs 4 AWG Copper
Going from 6 AWG to 4 AWG adds 20A of capacity and extends maximum wire run distance before hitting the 3% voltage drop limit. The trade-off is cost: 4 AWG copper costs more per foot and requires a larger conduit (1" EMT vs 3/4" EMT).
Specification comparison
Side-by-side specifications per NEC 2023 for THHN copper conductors.
| Property | 6 AWG | 4 AWG |
|---|---|---|
| 90°C ampacity | 75A | 95A |
| Usable ampacity | 65A | 85A |
| Standard breaker | 70A | 90A |
| Conduit (EMT) | 3/4" EMT | 1" EMT |
Voltage drop crossover
At what distance does 6 AWG fail the 3% recommendation and 4 AWG still passes? This shows the distance where upsizing is required, not optional.
Load: 65A on 240V single-phase.
| Distance | 6 AWG | 4 AWG | Verdict |
|---|---|---|---|
| 25 ft | 0.7% | 0.4% | Either works |
| 50 ft | 1.3% | 0.8% | Either works |
| 75 ft | 2.0% | 1.2% | Either works |
| 100 ft | 2.7% | 1.7% | Either works |
| 125 ft | 3.3% | 2.1% | Upsize to 4 |
| 150 ft | 4.0% | 2.5% | 4 still OK |
| 200 ft | 5.3% | 3.3% | Both exceed 3% |
| 250 ft | 6.7% | 4.2% | Both exceed 3% |
| 300 ft | 8.0% | 5.0% | Both exceed 3% |
When to upsize
Stay with 6 AWG when
- Circuit load is within 65A capacity
- Wire run is short (under ~112 ft at 240V)
- Budget is the primary constraint
Upsize to 4 AWG when
- You need more than 65A (loads up to 85A)
- Wire run is long and voltage drop is a concern
- Future load growth is expected on this circuit
Detailed ampacity: 6 AWG copper, 4 AWG copper. Material comparison: 6 AWG Cu vs Al, 4 AWG Cu vs Al.
Frequently asked questions
Can I use 6 AWG instead of 4 AWG?
Only if your load is 65A or less and your wire run is short enough to stay within 3% voltage drop. 6 AWG carries 65A maximum. If you need more than 65A, or your run exceeds the distance limit, you must use 4 AWG or larger.
How much more does 4 AWG cost than 6 AWG?
4 AWG typically costs 40-60% more per foot than 6 AWG for the same insulation type. The larger wire also requires larger conduit (1" EMT vs 3/4" EMT). However, the lower voltage drop can save energy on long runs.
What to buy
If you are buying wire for a new installation, consider your total project requirements. For 6 AWG: buy NM-B cable for in-wall residential or individual THHN conductors for conduit. For 4 AWG: same insulation types apply but expect approximately 40-60% higher cost per foot. When in doubt about which gauge, upsize: the cost of the wire is a small fraction of the total project cost (labor, conduit, breaker, permits), and upgrading later means repulling the entire run.
Common products for 4 AWG Copper circuits
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NEC 2023 references verified April 2026