Calculator
Formula Used
Resistance: R = ρL / A
Temperature correction: ρT = ρref × [1 + α × (T - Tref)]
Parallel conductors: Rtotal = Rsingle / n
Voltage drop: Vdrop = I × Rtotal
Power loss: P = I² × Rtotal
Here, R is resistance, ρ is resistivity, L is length, A is area, α is the temperature coefficient, and n is the number of equal parallel conductors.
How To Use This Calculator
Select a material preset or choose custom material. Enter resistivity when custom material is selected. Add the conductor length and its unit. Choose the area method. Enter known area, diameter, strand data, or AWG size. Add temperatures for correction. Enter current and voltage if voltage drop and heat loss are needed. Press Calculate. Use the CSV or PDF buttons to export the same result.
Example Data Table
| Material | Length | Area | Resistivity | Approximate Resistance |
|---|---|---|---|---|
| Copper | 10 m | 2.5 mm² | 1.724e-8 Ω·m | 0.06896 Ω |
| Aluminum | 10 m | 2.5 mm² | 2.82e-8 Ω·m | 0.1128 Ω |
| Nichrome | 1 m | 0.5 mm² | 1.10e-6 Ω·m | 2.2 Ω |
Understanding Resistance From Resistivity
Resistance links material behavior, conductor length, and cross sectional area. A longer path makes charge flow harder. A wider path gives charges more room. Resistivity describes how strongly a material opposes current. Copper has low resistivity. Nichrome has much higher resistivity. That difference matters when choosing wires, heaters, bus bars, sensors, and test leads.
Why The Inputs Matter
The calculator starts with resistivity. You may select a common material, or enter a custom value. Then it converts length and area to SI units. Area can come from a known section, a round diameter, strands, or AWG. This helps compare many conductor shapes. The tool also allows parallel conductors. Identical conductors in parallel reduce total resistance.
Temperature Correction
Most metals change resistance with temperature. The temperature coefficient estimates that change from a reference temperature. A positive coefficient increases resistance when the conductor becomes warmer. This is useful for long feeders, coils, shunts, and heated elements. The linear model is simple. It works best near the reference temperature. For extreme heat, use manufacturer data.
Design Checks
Resistance is not only a number. It affects voltage drop and power loss. A small resistance can still waste power when current is high. The calculator can estimate voltage drop, drop percentage, conductance, and heat loss. These values help you judge efficiency and safety. They also support early design choices before detailed standards are applied.
Good Practice
Use measured dimensions when possible. Nominal wire sizes can vary by standard. Include connector length when it is important. Check insulation temperature ratings separately. This calculator gives engineering estimates, not a code approval. Always confirm final conductor sizing with local rules, equipment limits, and tested material data.
Result Accuracy
Use consistent units before comparing results. A mistake in area units can change resistance by a million times. Square millimeters and square meters are very different. The form shows converted area to reduce that risk. Scientific notation is useful for small resistances. It keeps long feeder and bus calculations readable. For installed circuits, also consider skin effect at high frequency. Include joints, terminals, and fuses when they add meaningful resistance. Recheck every value after exporting reports. Document assumptions so reviews stay clear and practical for everyone.
FAQs
What is resistivity?
Resistivity is a material property. It shows how strongly a material resists electric current. Lower resistivity gives lower resistance for the same length and area.
What formula does this calculator use?
It uses R = ρL / A. It also applies optional temperature correction with ρT = ρref × [1 + α × (T - Tref)].
Why does longer wire have more resistance?
A longer wire gives electrons a longer path. More path length creates more opposition to current. So resistance rises directly with length.
Why does larger area reduce resistance?
A larger cross sectional area gives current more room to flow. That reduces opposition. Resistance is inversely proportional to conductor area.
Can I calculate resistance from diameter?
Yes. Select the diameter method. The calculator converts diameter to circular area using A = πd² / 4, then applies the resistance formula.
Does temperature affect resistance?
Yes. Many metals increase resistance when temperature rises. The coefficient input estimates this change from the reference temperature.
How are parallel conductors handled?
The calculator assumes equal conductors in parallel. It divides single conductor resistance by the number of parallel conductors.
Is this suitable for final electrical design?
Use it for estimates and learning. Final conductor sizing should follow local electrical rules, equipment ratings, installation conditions, and manufacturer data.