Wire Gauge Calculator

Calculate the right wire size for your electrical project

Recommended Gauge

10 AWG

Voltage Drop

2.07%

Actual Voltage

117.5V

Power Loss

50W

Unit System

Load (Amps)

Check equipment nameplate or breaker rating

System Voltage

Phase

One-Way Distance (feet)

Distance from panel to load (not round trip)

Wire Material

Max Voltage Drop (%)

NEC recommends 3% max for branch circuits

Recommended Gauge

10 AWG

5.26 mm²

Voltage Drop

2.07%

2.48V

Voltage at Load

117.5V

of 120V

Power Loss

50W

I × VD

Voltage Drop

2.07% drop (2.48V)21%

Excellent (<3%)Acceptable (3-5%)Excessive (>5%)

Wire Gauge Reference Chart

AWG	mm²	Cu Amps	Al Amps
14	2.08	15A	-
12	3.31	20A	15A
10	5.26	30A	25A
8	8.37	40A	35A
6	13.3	55A	45A
4	21.2	70A	60A
3	26.7	85A	70A
2	33.6	95A	85A
1	42.4	110A	95A
1/0	53.5	125A	110A

Ampacity based on NEC Table 310.16 (75°C rating)

Acceptable Configuration

• Always follow local electrical codes and permit requirements
• Turn off power before working on electrical circuits
• Consult a licensed electrician for permanent installations
• Consider derating factors for high temperatures or bundled wires
• This calculator provides guidance only, not professional advice

Example Calculations

120A Kitchen Circuit (Copper, 120V, 50 ft)

Inputs

Load20 Amps

Voltage120V

Distance50 feet

MaterialCopper

PhaseSingle-phase

Max Drop3%

Result

Recommended Wire10 AWG

Voltage Drop2.48V (2.07%)

Voltage at Load117.5V

12 AWG has 1.98 ohms/1000ft resistance. VD = (2 × 50 × 1.98 × 20) / 1000 = 3.96V = 3.3% -- exceeds 3% limit. 10 AWG has 1.24 ohms/1000ft. VD = (2 × 50 × 1.24 × 20) / 1000 = 2.48V = 2.07% -- acceptable. Recommended: 10 AWG.

230A Subpanel Feed (Aluminum, 240V, 100 ft)

Inputs

Load30 Amps

Voltage240V

Distance100 feet

MaterialAluminum

PhaseSingle-phase

Max Drop3%

Result

Recommended Wire6 AWG

Voltage Drop4.71V (1.96%)

Voltage at Load235.3V

8 AWG aluminum: resistance = 0.778 × 1.6 = 1.245 ohms/1000ft. VD = (2 × 100 × 1.245 × 30) / 1000 = 7.47V = 3.11% -- exceeds 3%. 6 AWG aluminum: resistance = 0.491 × 1.6 = 0.786 ohms/1000ft. VD = (2 × 100 × 0.786 × 30) / 1000 = 4.71V = 1.96% -- acceptable.

Show all examples

Frequently Asked Questions

How do I choose the right wire gauge?

Wire gauge depends on amperage (current draw), distance, and acceptable voltage drop. Higher amperage needs thicker wire (lower AWG number). Longer distances need thicker wire to prevent excessive voltage drop.

15A circuit: Minimum 14 AWG copper (most lighting and receptacles)
20A circuit: Minimum 12 AWG copper (kitchen, bathroom, garage)
30A circuit: Minimum 10 AWG copper (dryers, water heaters)
40A circuit: Minimum 8 AWG copper (ranges, large appliances)
50A+ circuit: Minimum 6 AWG copper (subpanels, EV chargers)

Circuit Amps	Min Copper AWG	Max Distance (3% drop, 120V)	Common Use
15A	14 AWG	50 ft	Lighting, receptacles
20A	12 AWG	40 ft	Kitchen, bathroom
30A	10 AWG	30 ft	Dryer, water heater
40A	8 AWG	25 ft	Range, cooktop
50A	6 AWG	20 ft	Subpanel, EV charger

What is voltage drop and why does it matter?

Voltage drop is the loss of electrical pressure as current travels through wire. Excessive drop (>3% for branch circuits, >5% total) causes equipment malfunction, dimming lights, and wasted energy. Longer runs need thicker wire.

NEC recommends max 3% drop for branch circuits (3.6V on 120V)
NEC recommends max 5% total from panel to load (6V on 120V)
Every doubling of distance doubles the voltage drop
Going up one wire size (e.g., 12 to 10 AWG) cuts drop by ≈40%
At 240V, the same wire carries the same amps with half the % drop

What wire size for 20 amps?

For a 20-amp circuit, use 12 AWG wire for runs up to 50 feet. For longer distances, consider 10 AWG to minimize voltage drop. Always follow local electrical codes.

12 AWG copper: Safe for 20A up to 50 ft (2.9% drop at 120V)
10 AWG copper: Better for 50–100 ft runs (1.8% drop at 50 ft)
12 AWG resistance: 1.98 ohms per 1,000 ft
10 AWG resistance: 1.24 ohms per 1,000 ft
NEC Table 310.16: 12 AWG rated for 20A at 60°C termination

What is the difference between AWG and mm²?

AWG (American Wire Gauge) is used in North America - lower numbers mean thicker wire. mm² is the metric standard measuring cross-sectional area. For example: 14 AWG ≈ 2.08 mm², 12 AWG ≈ 3.31 mm².

14 AWG = 2.08 mm² = 1.63 mm diameter
12 AWG = 3.31 mm² = 2.05 mm diameter
10 AWG = 5.26 mm² = 2.59 mm diameter
8 AWG = 8.37 mm² = 3.26 mm diameter
Each 3 AWG steps doubles the cross-sectional area

AWG	mm²	Diameter (mm)	Ampacity (Copper, 60°C)
14 AWG	2.08 mm²	1.63 mm	15A
12 AWG	3.31 mm²	2.05 mm	20A
10 AWG	5.26 mm²	2.59 mm	30A
8 AWG	8.37 mm²	3.26 mm	40A
6 AWG	13.30 mm²	4.11 mm	55A
4 AWG	21.15 mm²	5.19 mm	70A

Should I use copper or aluminum wire?

Copper is more conductive, smaller, and easier to work with. Aluminum is cheaper but requires larger gauges for the same ampacity. Aluminum also needs special connectors and is typically used only for service entrances and feeders.

Copper conductivity: 100% IACS (reference standard)
Aluminum conductivity: 61% IACS (needs 1.6× larger cross-section)
Copper cost: ≈$3.50–$5.00/ft for 6 AWG
Aluminum cost: ≈$1.50–$2.50/ft for equivalent 4 AWG
Aluminum requires anti-oxidant compound and rated connectors (AL/CU)

Property	Copper	Aluminum
Conductivity	100% IACS	61% IACS
Size for 100A	3 AWG	1 AWG
Cost (per ft, 100A)	$4–$7	$2–$4
Weight (per ft)	Heavier	70% lighter
Typical Use	Branch circuits	Service entrance, feeders

AWG

mm²

Cu Amps

Al Amps

2.08

15A

3.31

20A

15A

5.26

30A

25A

8.37

40A

35A

13.3

55A

45A

21.2

70A

60A

26.7

85A

70A

33.6

95A

85A

42.4

110A

95A

1/0

53.5

125A

110A

Example Calculations

120A Kitchen Circuit (Copper, 120V, 50 ft)

Inputs

Load20 Amps

Voltage120V

Distance50 feet

MaterialCopper

PhaseSingle-phase

Max Drop3%

Result

Recommended Wire10 AWG

Voltage Drop2.48V (2.07%)

Voltage at Load117.5V

230A Subpanel Feed (Aluminum, 240V, 100 ft)

Inputs

Load30 Amps

Voltage240V

Distance100 feet

MaterialAluminum

PhaseSingle-phase

Max Drop3%

Result

Recommended Wire6 AWG

Voltage Drop4.71V (1.96%)

Voltage at Load235.3V

Show all examples

Frequently Asked Questions

How do I choose the right wire gauge?

15A circuit: Minimum 14 AWG copper (most lighting and receptacles)
20A circuit: Minimum 12 AWG copper (kitchen, bathroom, garage)
30A circuit: Minimum 10 AWG copper (dryers, water heaters)
40A circuit: Minimum 8 AWG copper (ranges, large appliances)
50A+ circuit: Minimum 6 AWG copper (subpanels, EV chargers)

Circuit Amps	Min Copper AWG	Max Distance (3% drop, 120V)	Common Use
15A	14 AWG	50 ft	Lighting, receptacles
20A	12 AWG	40 ft	Kitchen, bathroom
30A	10 AWG	30 ft	Dryer, water heater
40A	8 AWG	25 ft	Range, cooktop
50A	6 AWG	20 ft	Subpanel, EV charger

What is voltage drop and why does it matter?

NEC recommends max 3% drop for branch circuits (3.6V on 120V)
NEC recommends max 5% total from panel to load (6V on 120V)
Every doubling of distance doubles the voltage drop
Going up one wire size (e.g., 12 to 10 AWG) cuts drop by ≈40%
At 240V, the same wire carries the same amps with half the % drop

What wire size for 20 amps?

For a 20-amp circuit, use 12 AWG wire for runs up to 50 feet. For longer distances, consider 10 AWG to minimize voltage drop. Always follow local electrical codes.

12 AWG copper: Safe for 20A up to 50 ft (2.9% drop at 120V)
10 AWG copper: Better for 50–100 ft runs (1.8% drop at 50 ft)
12 AWG resistance: 1.98 ohms per 1,000 ft
10 AWG resistance: 1.24 ohms per 1,000 ft
NEC Table 310.16: 12 AWG rated for 20A at 60°C termination

What is the difference between AWG and mm²?

14 AWG = 2.08 mm² = 1.63 mm diameter
12 AWG = 3.31 mm² = 2.05 mm diameter
10 AWG = 5.26 mm² = 2.59 mm diameter
8 AWG = 8.37 mm² = 3.26 mm diameter
Each 3 AWG steps doubles the cross-sectional area

AWG	mm²	Diameter (mm)	Ampacity (Copper, 60°C)
14 AWG	2.08 mm²	1.63 mm	15A
12 AWG	3.31 mm²	2.05 mm	20A
10 AWG	5.26 mm²	2.59 mm	30A
8 AWG	8.37 mm²	3.26 mm	40A
6 AWG	13.30 mm²	4.11 mm	55A
4 AWG	21.15 mm²	5.19 mm	70A

Should I use copper or aluminum wire?

Copper conductivity: 100% IACS (reference standard)
Aluminum conductivity: 61% IACS (needs 1.6× larger cross-section)
Copper cost: ≈$3.50–$5.00/ft for 6 AWG
Aluminum cost: ≈$1.50–$2.50/ft for equivalent 4 AWG
Aluminum requires anti-oxidant compound and rated connectors (AL/CU)

Property	Copper	Aluminum
Conductivity	100% IACS	61% IACS
Size for 100A	3 AWG	1 AWG
Cost (per ft, 100A)	$4–$7	$2–$4
Weight (per ft)	Heavier	70% lighter
Typical Use	Branch circuits	Service entrance, feeders

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