Wire Size Chart: AWG, Amps, mm² & Wire Sizing Guide

A wire size chart gives you a quick way to compare American Wire Gauge (AWG) sizes, conductor diameter, cross sectional area and ampacity. But a chart is only a starting point: the correct wire for an actual circuit also depends on load current, conductor material, temperature, installation conditions, overcurrent protection and voltage drop.

For US electrical work, this guide focuses on AWG sizes and NEC based concepts. Use the chart for reference then verify the final conductor selection against the electrical conditions and the NEC edition adopted by the authority having jurisdiction (AHJ).

Key Takeaways

A wire chart is useful for quick comparison but it should not be treated as a universal wire sizing rule.

Lower AWG Numbers Mean Larger Wires

In the American Wire Gauge system, a lower number means a larger conductor. For example, 10 AWG is larger than 14 AWG.

Ampacity Is Not the Same as Breaker Size

The ampacity listed in a conductor table is affected by temperature rating, installation conditions and other requirements. Small conductor overcurrent rules can also limit the permitted protection.

Longer Runs May Need Larger Wire

A conductor can have enough ampacity for a load but still produce excessive voltage drop over a long distance.

Copper and Aluminum Are Different

The same AWG size does not have the same electrical characteristics for copper and aluminum conductors.

A Chart Is a Starting Point

For an actual installation, check ampacity, overcurrent protection, voltage drop, conductor temperature, installation method and applicable code requirements.

Wire Size Chart: AWG, mm², Diameter and Ampacity

The table below provides a quick reference for common US building wire sizes. The copper and aluminum ampacity columns use the 75°C values associated with NEC Table 310.16 under its base conditions: not more than three current carrying conductors in a raceway, cable or directly buried in earth at a 30°C (86°F) ambient.

Note: These table ampacities do not automatically mean that a circuit can be protected at the same ampere value. NEC 240.4(D) places additional overcurrent protection limits on small copper conductors including 15 A for 14 AWG, 20 A for 12 AWG and 30 A for 10 AWG under the applicable rule.

The Table 310.16 values are reference values not universal installation ratings. Ambient temperature, the number of current carrying conductors, conductor insulation and terminal limitations can change the allowable ampacity.

How to Read an Electrical Wire Size Chart?

A wire size chart normally contains several measurements because wire size can mean different things.

AWG

AWG stands for American Wire Gauge. It is the sizing system commonly used for electrical conductors in the United States. The important rule is:

Lower AWG number = larger conductor

For example:

Once conductor sizes reach 1/0, 2/0, 3/0 and 4/0 the number increases as the conductor becomes larger.

• 14 AWG is smaller than 12 AWG.
• 12 AWG is smaller than 10 AWG.
• 10 AWG is smaller than 8 AWG.
• 4 AWG is smaller than 2 AWG.

mm²

The mm² value represents the conductor's cross sectional area. Unlike AWG the metric system gets larger as the number gets larger:

Larger mm² = larger conductor

For example a 10 mm² conductor has a larger cross sectional area than a 6 mm² conductor. AWG and mm² are not exact one to one equivalents. A metric conductor should therefore be selected according to its actual specification rather than simply treating a rounded conversion as identical.

Diameter

Diameter describes the physical width of the conductor itself. A larger conductor generally has a larger diameter and greater cross sectional area although the outside diameter of a finished insulated wire or cable is also affected by insulation, jacket and construction.

Wire Size Chart in Inches and Millimeters

AWG charts often provide both millimeter and inch measurements. Some common conductor diameters are approximately:

These are conductor dimensions, not the overall outside diameter of an insulated cable. That distinction matters when checking conduit fill, cable routing or physical installation space.

What Is Wire Ampacity?

Ampacity is the amount of current a conductor can carry under specified conditions without exceeding its allowable temperature. This is why a wire size chart may show several ampacity values for the same conductor.

For example copper conductors can have different values at 60°C, 75°C and 90°C. A 10 AWG copper conductor is listed at different ampacities in those temperature columns but that does not mean you can simply select the highest number for every installation.

The applicable conductor insulation, termination ratings and installation conditions must be considered together. NEC 110.14(C) places limits on the temperature column that can be used for equipment terminations.

Wire Size by Amps: Quick Reference

People often search for a wire size chart by amps because they already know the circuit current. For a short simple US branch circuit application with common copper conductors, the familiar starting points are:

These should be treated as reference starting points not universal wire size recommendations. The actual answer can change because of continuous loads, conductor temperature, adjustment and correction factors, application specific NEC rules, voltage drop and the equipment's termination requirements.

For example a 20A load on a very long circuit may require a larger conductor than a short 20A circuit because voltage drop can become the limiting factor.

Why 12 AWG Is Not Simply a 25 Amp Wire

This is one of the most important points when reading an electrical wire size chart. Under the 75°C column, 12 AWG copper has a tabulated ampacity of 25 A. However NEC 240.4(D) limits the overcurrent protection for 12 AWG copper to 20 A under the applicable small conductor rule.

The same issue appears with:

This is why an ampacity chart and a breaker to wire chart are not exactly the same thing.

• 14 AWG copper: 20 A at 75°C but 15 A OCPD limit under the small conductor rule.
• 12 AWG copper: 25 A at 75°C but 20 A OCPD limit.
• 10 AWG copper: 35 A at 75°C but 30 A OCPD limit.

How to Calculate Wire Size for Amps?

If you are trying to choose a conductor for a real circuit do not start by looking for one exact amps = AWG answer. Use this general process.

1. Determine the Actual Load Current

Start with the equipment nameplate or the calculated electrical load. If the equipment rating is given in watts and the load is suitable for a simple approximation current can be estimated from:

I = P ÷ V

Where:

For motors and other non resistive loads do not assume watts divided by volts always give the actual running current. Power factor, efficiency and starting conditions can matter.

• I = current in amps
• P = power in watts
• V = voltage in volts

2. Account for Continuous Loads

A continuous load can require additional capacity under the applicable electrical rules. For a common 125% calculation:

Required ampacity = 125% × continuous load + noncontinuous load

The exact rule depends on the circuit and applicable NEC section.

3. Check the Ampacity Table

Compare the required ampacity with the appropriate conductor ampacity. Do not simply select the 90°C value because it is the largest number in the chart.

4. Apply Correction and Adjustment Factors

Temperature and conductor grouping can reduce allowable ampacity. Important factors can include:

NEC Table 310.16 is based on specific reference conditions so the tabulated number may need adjustment for the actual installation.

• Ambient temperature
• Number of current carrying conductors
• Conductor insulation rating
• Raceway or cable conditions
• Termination temperature
• Installation method

5. Check Voltage Drop

After ampacity is satisfied check voltage drop when the circuit length or application makes it important. A wire can have adequate ampacity but still be too small for a long run because its resistance produces excessive voltage loss. For a general voltage drop calculation use our Voltage Drop Calculator .

Why Wire Size Depends on Distance

Current is not the only factor that affects conductor selection. As conductor length increases, total resistance also increases. At the same current greater resistance produces greater voltage drop.

This is why two circuits carrying the same 20A load can require different conductor sizes. A short 20A branch circuit may work with the normal minimum conductor size while a much longer 20A run may need a larger conductor to maintain the desired load end voltage.

The same principle becomes especially important in:

For a specific run our Voltage Drop Calculator for Wire & Cable Size can be used to evaluate voltage loss separately from the ampacity check.

• Detached buildings
• Long feeder runs
• Solar systems
• 12V and 24V DC systems
• Landscape lighting
• Pumps
• Motors
• Outdoor equipment

Wire Size Chart vs Voltage Drop Calculation

These two tools answer different questions. A wire size chart primarily gives you reference information about conductor size and ampacity. A voltage drop calculation asks how much voltage is lost along a particular conductor run.

For example imagine two 12 AWG copper circuits carrying the same current. One is 20 feet long. The other is 200 feet long.

The conductor size is identical but the longer circuit has substantially more conductor resistance and therefore potentially much more voltage drop.

That is why final conductor selection should consider both ampacity and voltage drop where applicable. For the underlying calculation method see our Voltage Drop Formula and Calculation Table .

Copper vs Aluminum Wire Size

Copper and aluminum conductors of the same AWG size do not have identical electrical characteristics. Copper generally has lower resistance for the same cross sectional area while aluminum is lighter and commonly used for larger feeders and service conductors. The wire chart therefore should not be interpreted as:

This AWG always carries exactly this current. Instead identify:

Then determine the allowable ampacity. The 75°C values in the reference chart above show why copper and aluminum columns should be kept separate.

• Conductor material
• Conductor type
• Insulation temperature rating
• Installation conditions
• Terminal ratings
• Applicable code requirements

When Should You Use a Wire Size Calculator Instead?

A chart is useful when you need a quick reference. A calculator becomes more useful when the actual installation has several variables. Use a wire size calculator when you need to account for things such as:

A fixed chart cannot know those details. For example our Solar Wire Size Calculator guide explains why solar conductor sizing depends on system voltage, current, distance, configuration and voltage drop rather than one fixed chart value.

Similarly feeder applications require a separate load and conductor sizing process rather than simply choosing a wire from an amp chart. Our Feeder Size Calculator guide covers that application separately.

• Load current
• Voltage
• Cable length
• Conductor material
• Voltage drop target
• Ampacity
• Temperature
• Installation conditions

Common Wire Sizing Mistakes

Choosing Wire From Amps Alone

Current is important but it does not tell you everything about the conductor. Distance, installation conditions, temperature and voltage drop can change the final selection.

Treating Ampacity as Breaker Size

The number in an ampacity table is not automatically the permitted breaker rating. Small conductor rules are a common example of why the two values must be checked separately.

Using the 90°C Column as the Final Answer

A 90°C insulation rating does not automatically mean the circuit can be sized using the 90°C ampacity. Termination ratings and applicable code rules can limit the final value.

Ignoring Voltage Drop

A conductor can satisfy an ampacity requirement and still produce too much voltage loss on a long run.

Treating AWG and mm² as Exact Equivalents

AWG and metric conductor areas are different sizing systems. Use the actual conductor specification instead of assuming every rounded conversion is identical.

Ignoring Installation Conditions

A chart assumes particular conditions. Actual ambient temperature, conductor grouping and installation method may require corrections or adjustments.

Does a Bigger Wire Always Carry More Current?

Generally a larger conductor has greater current carrying capability under comparable conditions because its larger cross sectional area reduces resistance and heat generation.

However conductor size alone does not determine the final allowable current. The conductor material, insulation, installation conditions, temperature, terminations and applicable electrical requirements all matter.

What Wire Size Is Used for a House?

There is no single wire size for an entire house. Residential circuits commonly use several conductor sizes depending on the circuit load and application.

For example 14 AWG and 12 AWG copper are common on smaller branch circuits while larger conductors are used for higher current equipment, feeders and services.

The correct size must be determined from the specific circuit rather than assuming that one house wire size applies everywhere.

Does 240V Need Smaller Wire Than 120V?

Not automatically. For the same power increasing voltage reduces current:

I = P ÷ V

So a 2,400W load would theoretically draw:

Lower current can reduce conductor requirements and voltage drop percentage but the final wire size still depends on the circuit design, ampacity, protection, distance and applicable electrical requirements.

• 20 A at 120 V
• 10 A at 240 V

What About the 2026 NEC?

The 2026 NEC introduced changes to the smallest conductor sizes and added new Table 310.16 entries including values for 16 AWG copper and 14 AWG copper clad aluminum. The core ampacity values for the common 8 AWG through 4/0 AWG sizes used in this chart remain unchanged.

Because NEC adoption varies by jurisdiction, always use the edition adopted by the AHJ for the project. This is particularly important when a chart is being used for actual installation or permit work.

When a Wire Size Chart Is Not Enough

A wire chart is a useful reference but it should not replace a complete electrical design check. You may need additional calculations for:

For these applications use the chart to understand the conductor sizes then perform the calculations required for the actual installation.

• Long conductor runs
• Continuous loads
• Motors
• HVAC equipment
• Feeders
• Services
• Solar and battery systems
• Parallel conductors
• High ambient temperatures
• Multiple current carrying conductors
• Special equipment
• Voltage sensitive loads

Conclusion

A wire size chart is one of the quickest ways to compare AWG, mm², conductor diameter and ampacity. For US electrical work however the chart should be treated as a reference rather than a universal answer.

Start with the actual load, determine the required ampacity, apply the relevant temperature and installation rules, check overcurrent protection and evaluate voltage drop when the circuit length or application requires it.

The most important distinction is simple: ampacity tells you how much current a conductor can carry under specified conditions while voltage drop calculations tell you how much voltage is lost along the run. A correct wire selection may need both checks.

FAQs

What is the most common wire size for a 20 amp circuit?

12 AWG copper is the common starting point for a 20A branch circuit under the applicable small conductor rule. The final installation still needs to satisfy all applicable requirements.

What size wire do I need for 30 amps?

10 AWG copper is a common starting point for a 30A circuit. Actual conductor selection can change depending on conductor type, temperature, installation conditions and the specific application.

How do I calculate wire size for amps?

Determine the load current, account for continuous loads where applicable, select a conductor with sufficient allowable ampacity, apply correction and adjustment factors, check overcurrent protection and evaluate voltage drop when necessary.

What is the difference between AWG and mm²?

AWG is the American Wire Gauge system while mm² describes conductor cross sectional area. They are different sizing systems and do not have exact one to one equivalents.

Does a longer wire need to be a larger size?

Not necessarily for every installation but longer runs can require a larger conductor because resistance increases with length and voltage drop can become the limiting factor.

Is 12 AWG always good for 20 amps?

12 AWG copper is commonly used for 20A branch circuits but 12 AWG = 20A everywhere is too simplistic. The conductor installation conditions, overcurrent protection and applicable electrical rules still need to be checked.

Is the 75°C ampacity the actual current a wire can always carry?

No. The 75°C value is a tabulated ampacity under specified conditions. The applicable termination temperature, ambient temperature, conductor grouping and other requirements can change the allowable ampacity.