Standard Copper Wire Resistance Calculator

Calculator Inputs

Wire length

Length unit

Wire size method

AWG size

Diameter mm

Area mm²

Copper type

Custom resistivity nΩ·m

Conductor temperature C

Temperature coefficient per C

Stranding adjustment %

Parallel runs

Circuit path

Load current A

Supply voltage V

Connection resistance mΩ

Decimal precision

Formula Used

The calculator corrects copper resistivity for temperature, then applies the conductor resistance formula.

R = ((rho20 * (1 + alpha * (T - 20))) * L / A) * (1 + S / 100) / P

Rcircuit = (R * M) + Rconnection

Here, rho20 is copper resistivity at 20 C, alpha is the temperature coefficient, T is conductor temperature, L is length in meters, A is area in square meters, S is stranding adjustment percent, P is parallel runs, and M is the path multiplier.

How To Use This Calculator

Enter the measured wire length and choose its unit.
Select AWG, diameter, or area as the wire size method.
Choose the copper type or enter a custom resistivity value.
Set the conductor temperature and coefficient for correction.
Add current and voltage to estimate voltage drop and loss.
Choose round trip when both outgoing and return paths matter.
Press calculate, or download the same result as CSV or PDF.

Example Data Table

Wire size	Length	Temperature	Current	Path	Approximate circuit resistance	Voltage drop
14 AWG	50 ft	20 C	10 A	Round trip	0.253 Ω	2.53 V
12 AWG	100 ft	20 C	15 A	Round trip	0.318 Ω	4.77 V
10 AWG	75 ft	30 C	20 A	Round trip	0.191 Ω	3.82 V
2.5 mm²	30 m	25 C	12 A	Round trip	0.419 Ω	5.03 V

Electrical Planning With Copper Resistance

Copper wire is popular because it conducts current well. It still has resistance. That resistance grows with length. It falls when the wire area becomes larger. Heat also matters. Warm copper resists current more than cool copper. A good estimate helps before a cable is ordered, installed, or tested.

Why Accurate Resistance Matters

Small resistance can create real voltage drop. The drop may look minor on a short lead. It can become serious on a long feeder, battery cable, motor circuit, or solar run. Extra resistance also turns electrical energy into heat. This heat wastes power. It can reduce equipment performance. It can also make troubleshooting harder.

Useful Inputs

This calculator accepts several wire size methods. You can choose an AWG size. You can enter a diameter in millimeters. You can enter a known cross sectional area. Length can be entered in meters, feet, or kilometers. Temperature correction is included, because copper resistance is normally referenced at twenty degrees Celsius. You may also set current and source voltage. Those values show voltage drop and power loss.

Advanced Adjustments

Real wiring is not always a perfect single solid conductor. Stranded conductors may have slightly higher effective resistance. Parallel runs share current and lower total resistance. A round trip circuit uses the outgoing and returning conductor length. Terminations and lugs can add small resistance. These options help the estimate match field conditions.

Reading The Results

The main resistance result is the circuit resistance. It includes the selected route multiplier and extra connection resistance. The one conductor value is useful for catalog checks. Ohms per meter and ohms per thousand feet help compare wire sizes. Voltage drop percent helps judge whether the chosen wire is suitable for a load.

Best Use

Use this page for design checks, repair notes, lab comparisons, and quick estimates. Always confirm final wiring decisions with local codes, equipment manuals, and rated ampacity tables. Resistance is only one part of safe conductor selection. Insulation type, ambient temperature, installation method, overcurrent protection, and mechanical durability must also be considered.

Keep Saved Records

Saved exports make repeat checks easier. They also document assumptions. Record each temperature, wire size, and load before changing a design or quote.

FAQs

What does this calculator measure?

It estimates copper wire resistance from length, size, temperature, and circuit path. It also estimates voltage drop, power loss, conductance, and resistance per distance.

Can I use AWG and metric sizes?

Yes. Choose AWG, diameter in millimeters, or area in square millimeters. The calculator converts the selected size into cross sectional area for the resistance formula.

Why does temperature change resistance?

Copper resistance increases as conductor temperature rises. The temperature coefficient adjusts resistivity from the common 20 C reference point to the entered operating temperature.

What is round trip path?

Round trip path includes the outgoing conductor and the return conductor. Use it for most two-wire circuits when voltage drop across the full circuit is needed.

What is stranding adjustment?

It is an optional percentage increase for practical conductor construction. Use zero for ideal solid wire, or add a small percentage when a stranded cable has higher effective resistance.

How do parallel runs affect resistance?

Parallel runs share current across multiple equal conductors. The calculator divides conductor resistance by the number of parallel runs entered, assuming equal length and size.

Is voltage drop the same as resistance?

No. Resistance is a conductor property for the entered setup. Voltage drop equals current multiplied by circuit resistance. Higher current creates more drop.

Can this replace electrical code checks?

No. Use it for estimates and comparisons. Final wiring must also consider ampacity, insulation rating, installation conditions, protection devices, and local electrical rules.