For standard residential copper branch circuits, the baseline wire AWG size to breaker mapping is: 14 AWG for 15A, 12 AWG for 20A, 10 AWG for 30A, 8 AWG for 40A, and 6 AWG for 55A/60A. However, pulling a single number from a chart without understanding temperature columns and conduit derating is the most common cause of failed electrical inspections and overheated terminations. This reference guide provides the complete NEC Table 310.16 ampacity data for copper conductors, explains exactly which column applies to your specific installation, and breaks down the derating math you need for real-world conduit runs.
How to Read the NEC Wire AWG Size Ampacity Table
The ampacity table below is sourced directly from NEC Table 310.16 (2023/2026 editions) for copper conductors. Before you pick a wire gauge, you must understand the three temperature columns. The ampacity of a wire is not a single fixed number; it changes based on the thermal rating of the insulation and the equipment terminations.
Per NEC 110.14(C), your circuit's maximum ampacity is limited by the lowest temperature rating of any connected device, termination, or conductor.
- 60°C Column: Use this for NM-B (Romex) cable, as its overall jacket is rated for 60°C, and for circuits 100A or less where the breaker/lug temperature rating is unmarked (common in older panels).
- 75°C Column: Use this for THWN wire in wet locations, and for most modern breakers and lugs explicitly marked 75°C. This is the default column for sizing THHN/THWN-2 in standard residential panels.
- 90°C Column: Use this only as the starting point for derating calculations (adjusting for ambient heat or multiple wires in a conduit). You generally cannot use the 90°C ampacity to size your breaker unless the entire system (breaker, lug, and wire) is rated 90°C, which is exceptionally rare in residential work.
The Master Wire AWG Size Chart (Copper, THHN/THWN-2)
Use the quick-jump links below to find the most commonly queried residential circuit sizes, or scroll through the complete table. The "Max Standard OCPD" column reflects the maximum standard overcurrent protective device (breaker/fuse) size permitted by NEC 240.4(B) and the small conductor limits of 240.4(D).
Quick-Jump Bookmarks: 15A (14 AWG) | 20A (12 AWG) | 30A (10 AWG) | 50A (6 AWG) | 100A (3 AWG)
| Wire AWG Size | 60°C Ampacity (NM-B) | 75°C Ampacity (THWN) | 90°C Ampacity (THHN) | Max Standard OCPD (Breaker) |
|---|---|---|---|---|
| 14 AWG | 15A | 20A | 25A | 15A |
| 12 AWG | 20A | 25A | 30A | 20A |
| 10 AWG | 30A | 35A | 40A | 30A |
| 8 AWG | 40A | 50A | 55A | 40A / 50A* |
| 6 AWG | 55A | 65A | 75A | 60A |
| 4 AWG | 70A | 85A | 95A | 80A |
| 3 AWG | 85A | 100A | 115A | 100A |
| 2 AWG | 95A | 115A | 130A | 110A |
| 1 AWG | 110A | 130A | 145A | 125A |
| 1/0 AWG | 125A | 150A | 170A | 150A |
| 2/0 AWG | 145A | 175A | 195A | 175A |
| 3/0 AWG | 165A | 200A | 225A | 200A |
| 4/0 AWG | 195A | 230A | 260A | 225A |
*Note: 8 AWG is limited to 40A for standard branch circuits, but NEC exceptions allow 50A for specific motor and HVAC compressor circuits where the manufacturer specifies it.
When the Base Table Fails: Derating and Real-World Limits
The chart above assumes ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a single raceway. When you deviate from this, the base table becomes dangerously optimistic.
How Derating Rows Modify the Base Value
When you pull more than three current-carrying conductors through a single conduit, the wires heat each other up. NEC Table 310.15(C)(1) requires you to multiply the wire's base ampacity by a derating factor. Crucially, you apply this derating factor to the 90°C column, even if your terminations are rated 75°C.
Worked Example: You are pulling two 240V circuits (4 hot wires total, neutrals don't count for balanced 240V loads) through a single 3/4" EMT conduit. You need a wire AWG size for a 50A breaker.
1. Standard 6 AWG THHN at 90°C is 75A.
2. Four current-carrying conductors require an 80% derating factor.
3. 75A × 0.80 = 60A derated ampacity.
4. Because 60A is greater than the 50A load, and the final termination at the 75°C lug (65A) is also higher than 50A, 6 AWG THHN is legal and safe. If you had blindly used the 75°C column (65A × 0.80 = 52A), you'd still pass, but using the 90°C column for derating is the code-compliant method that saves you from upsizing to 4 AWG unnecessarily.
What the Table Cannot Tell You
Ampacity charts only address thermal limits at the source. They completely ignore voltage drop. If you are running a 100A subpanel 150 feet away, 3 AWG copper will keep the wires from melting, but the voltage drop at the far end under full load will exceed the recommended 3% threshold, causing lights to dim and motors to overheat. For long runs, you must use a voltage drop calculator and typically upsize the wire AWG size by one or two gauges beyond what the ampacity chart demands.
Wire AWG Size FAQ: Long-Tail Questions Answered
What wire AWG size do I need for a 50 amp 240V EV charger?
For a continuous 50A load (like a hardwired Level 2 EV charger), the NEC requires the circuit to be rated for 125% of the continuous load, meaning you need a 60A breaker and wire sized for 60A. If you are using NM-B (Romex) cable in a wall, you must use 4 AWG copper (rated 70A at 60°C). If you are pulling individual THHN/THWN-2 conductors in conduit to a 75°C rated disconnect, 6 AWG copper (rated 65A at 75°C) is sufficient and much easier to bend.
Can I use the 90°C THHN ampacity column to size my breaker?
Almost never. While the wire insulation itself can withstand 90°C, the circuit breaker lugs and receptacle terminals in residential panels are almost universally rated for 75°C. Per NEC 110.14(C), the lowest temperature rating in the circuit dictates the maximum allowable ampacity for breaker sizing. You use the 90°C column strictly as a mathematical starting point for conduit derating and ambient temperature adjustments, but the final derated number cannot exceed the 75°C column's base limit for that wire AWG size.
Does the bare ground wire count toward conduit derating?
No. When calculating the number of current-carrying conductors for NEC Table 310.15(C)(1) derating, equipment grounding conductors (the bare copper or green wire) are explicitly excluded. They only carry current during a fault condition, not during normal operation, so they do not contribute to the steady-state heat buildup inside the conduit. However, the ground wire does count toward the physical conduit fill capacity calculations found in NEC Chapter 9, Table 1.
What size wire is needed for a 100 amp subpanel 150 feet away?
For the ampacity requirement alone, 3 AWG copper or 1/0 AWG aluminum is sufficient for a 100A feeder at 75°C. However, at 150 feet, a 100A load on 3 AWG copper will result in roughly a 4.5% voltage drop on a 240V circuit, which exceeds the 3% NEC recommendation for feeders. To keep voltage drop under 3% at full capacity, you must upsize to 1/0 AWG copper or 3/0 AWG aluminum. Always calculate voltage drop based on the actual anticipated continuous load, not just the breaker size, to avoid paying for unnecessarily massive wire.
