Copper Wire Resistance Chart: AWG Resistance Values Explained

A copper wire resistance chart helps electricians, engineers and DIY users quickly compare the resistance of different copper wire sizes. Resistance is measured in ohms (Ω) and is an important factor when selecting wire, estimating voltage drop and designing electrical circuits.

Copper wire resistance depends on several factors, including conductor size, wire length, temperature and construction type. A larger copper conductor has lower resistance, while a smaller conductor creates more resistance over the same distance.

This guide provides a practical reference for common American Wire Gauge (AWG) copper wire sizes, explains resistance values in ohms per foot and per 1000 feet and shows how resistance affects voltage drop calculations.

Key Takeaways

Larger copper wires have lower resistance

A thicker conductor provides more space for electrical current to flow, reducing resistance. In the AWG system a lower AWG number means a larger wire.

Wire length directly affects resistance

The longer electricity travels through a conductor the higher the total resistance becomes.

Copper resistance affects voltage drop

Higher resistance causes greater voltage loss along a conductor. Accurate resistance values help with proper wire sizing and voltage drop calculations.

Copper Wire Resistance Chart (AWG)

The table below shows approximate DC resistance values for common copper wire sizes. Actual resistance can vary depending on conductor temperature, manufacturing tolerances and whether the conductor is solid or stranded.

These values are useful for estimating conductor resistance in electrical calculations. For critical installations, always verify conductor specifications using manufacturer data and applicable electrical standards. Here is the simple wire size chart you can use for your reference.

What Is the Resistance of Copper Wire?

Electrical resistance is the opposition a conductor provides to the movement of electric current. It is measured in ohms (Ω).

Copper is widely used for electrical wiring because it has excellent conductivity and relatively low resistance compared with many other metals. The resistance of copper wire depends on:

The basic relationship is:

Longer wire = higher resistance

Larger wire = lower resistance

For example a 100 ft length of 14 AWG copper wire will have more resistance than the same length of 10 AWG copper wire.

• Conductor length
• Wire size
• Copper material properties
• Operating temperature
• Solid or stranded construction

Copper Wire Resistance Formula

Copper wire resistance can be estimated using the standard resistance formula:

R = ρ × L ÷ A

Where:

This formula explains why wire length and size have such a major effect on resistance. Understanding the voltage drop formula helps explain how conductor resistance and current affect the final voltage available at the load.

A longer conductor increases resistance because current must travel through more material. A larger conductor reduces resistance because it provides a wider path for current flow.

• R = resistance in ohms
• ρ = resistivity of copper material
• L = conductor length
• A = conductor cross sectional area

Copper Wire Resistance by Length

Electrical calculations often use resistance values expressed as:

These measurements allow electricians and engineers to estimate total conductor resistance for different cable lengths. For example:

A 12 AWG copper wire has approximately:

0.001588 ohms per foot

For a 50 ft conductor:

0.001588 × 50 = 0.0794 ohms

In a complete circuit remember that current usually travels through both the outgoing and return conductors. Therefore the total conductor length may be twice the one way distance.

• Ohms per foot
• Ohms per 1000 feet

Copper Wire Resistance Per 1000 Feet

Manufacturers commonly publish resistance values per 1000 feet because it provides a standard comparison between different wire sizes. Example comparison:

This shows that larger conductors have significantly lower resistance. Lower resistance is especially important for:

• Long distance circuits
• Higher current applications
• Systems where voltage drop must be minimized

How Wire Size Affects Copper Resistance?

The American Wire Gauge (AWG) system can sometimes seem confusing because smaller numbers represent larger wires.

For the same length and current:

Choosing the correct conductor size is important for electrical performance and efficiency and proper wire and cable size calculations help determine the right conductor for each application.

• A smaller wire creates more resistance
• A larger wire reduces resistance
• A larger wire generally produces less voltage drop

Solid vs Stranded Copper Wire Resistance

Copper conductors are available in both solid and stranded designs.

Solid Copper Wire

Solid wire contains one continuous copper conductor. Common characteristics:

• Simple construction
• Good mechanical strength
• Often used in fixed wiring applications

Stranded Copper Wire

Stranded wire contains multiple smaller copper strands combined together. Common characteristics:

The resistance difference between solid and stranded copper wire of the same size is usually small. However exact values may vary because of strand construction and manufacturing methods. For precise calculations use the resistance specifications provided by the wire manufacturer.

• More flexible
• Easier to route through tight spaces
• Common in flexible electrical applications

How Temperature Changes Copper Wire Resistance?

Copper resistance increases as conductor temperature rises. A resistance chart normally provides values at a specific reference temperature. When the wire becomes hotter, resistance increases slightly. Temperature effects are important in:

For general estimates chart values are useful. For engineering level calculations use the correct temperature conditions.

• High current circuits
• Long cable runs
• Industrial electrical systems
• Detailed voltage drop calculations

How Copper Wire Resistance Affects Voltage Drop?

Resistance directly affects voltage drop in an electrical circuit. The relationship is:

Voltage Drop = Current × Resistance

When wire resistance increases:

For example:

A 12V DC circuit uses:

The wire resistance is approximately:

0.001588 × 100 = 0.1588 ohms

Voltage drop:

10 amps × 0.1588 ohms = 1.588 volts

The load would receive approximately:

12V - 1.588V = 10.412V

This example shows why wire resistance is an important factor when selecting cable size. For more detailed calculations you can calculate voltage drop based on wire size, distance, current and conductor resistance using our Voltage Drop Calculator.

• More voltage is lost along the conductor
• The load receives less voltage
• Electrical efficiency decreases
• 100 ft total conductor length
• 10 amps current
• 12 AWG copper wire

How to Calculate Copper Wire Resistance?

To calculate copper wire resistance:

Step 1: Identify the wire size

Find the AWG size of the copper conductor.

Step 2: Find resistance value

Use a copper wire resistance chart to find ohms per foot or ohms per 1000 feet.

Step 3: Multiply by conductor length

Formula:

Total Resistance = Resistance per foot × Total Length

Step 4: Use resistance for electrical calculations

The resistance value can then be used to estimate voltage drop and circuit performance.

Conclusion

A copper wire resistance chart is a valuable reference for comparing electrical resistance across different conductor sizes. Wire gauge, length, temperature and conductor construction all influence resistance values.

Understanding copper wire resistance helps improve wire selection, voltage drop calculations and overall electrical system performance. For accurate electrical designs use verified conductor specifications and consider the actual operating conditions of the circuit.

FAQs

What is the resistance of copper wire?

Copper wire resistance depends on wire size, length and temperature. Larger copper conductors have lower resistance than smaller conductors of the same length.

How much resistance is acceptable in a wire?

Acceptable resistance depends on the electrical application, current level, circuit length and voltage requirements. The goal is usually to keep voltage drop within acceptable limits.

What is the resistance of copper wire per 1000 feet?

The resistance depends on wire size. For example 12 AWG copper wire is approximately 1.588 ohms per 1000 feet while 10 AWG copper wire is approximately 0.999 ohms per 1000 feet.

What is the resistance of 1.5 mm² copper wire?

A 1.5 mm² copper conductor is commonly referenced using metric conductor tables rather than AWG charts. Resistance depends on conductor temperature and construction but it is generally measured in ohms per kilometer.

Does copper wire resistance increase with length?

Yes. Resistance increases as conductor length increases because electrical current must travel through more material.