Please enter all required numeric values.
RESULTS
Input Parameters Specification
Wire Diameter DDiameter of each conductor in the twisted pair.
Spacing SCenter-to-center spacing between the two conductors.
Dielectric εrInsulation dielectric constant around the pair.
OutputsZo, delay, inductance and capacitance per inch.
Practical Operational Examples
Signal Cable Check
Use this calculator when estimating the impedance of a twisted pair used for digital communication, sensor wiring, or differential signal routing.
Dielectric Effect
A higher dielectric constant lowers characteristic impedance and increases propagation delay, which can matter in longer cable runs.
Diagrams & Theory
A twisted pair is made from two insulated conductors. Impedance depends mainly on conductor spacing, wire diameter and dielectric material.
Formulas & Mathematical Logic
Zo = (120 / sqrt(εr)) × ln(2S / D)
Delay = 84.72 × 10^-3 × sqrt(εr)
Inductance = 10.16 × ln(2S / D)
Capacitance = (0.7065 × εr) / ln(2S / D)
The calculator converts both diameter and spacing into the same internal inch-based scale before applying the impedance and per-inch parameter formulas.
Step-by-Step Example
Example: Wire diameter = 0.5 mm, spacing = 1.2 mm, dielectric constant εr = 2.25.
The selected units convert both geometry values to the same base scale.
The ratio 2S / D is calculated first, then ln(2S / D) is used in impedance, inductance, and capacitance formulas.
Higher spacing usually increases Zo and inductance; higher εr lowers Zo and increases capacitance and delay.
How to Use This Calculator
Enter the diameter of one conductor in the twisted pair.
Select the diameter unit: mil, mm, cm, µm, or inch.
Enter the center spacing between both conductors.
Enter dielectric constant εr for the insulation material.
Click Calculate to get Zo, delay, inductance, and capacitance per inch.
About This Calculator
Estimate twisted-pair electrical behavior from physical geometry.
The CalcBoy Twisted-Pair Impedance Calculator helps electronics users estimate characteristic impedance, delay, inductance, and capacitance for two insulated conductors.
Twisted-pair wiring is used because the two conductors stay close together and share a controlled return path. This helps reduce noise pickup, magnetic loop area, and unwanted radiation compared with separated wires. But the electrical behavior is still controlled by the conductor diameter, spacing, and insulation material. A small change in spacing or dielectric constant can shift impedance enough to matter in high-speed signals, sensor cables, differential interfaces, and communication wiring.
This calculator is useful for quick design checks when building custom cables, comparing wire geometry, or estimating whether a twisted pair is close to a target impedance. It is not a full field-solver, but it gives a practical first-pass estimate for cable delay, capacitance per inch, and inductance per inch.
Best UseQuick estimates for twisted-pair geometry, cable experiments, and differential signal wiring.
Helpful ForSensor leads, communication pairs, RF wiring, test cables, and embedded hardware projects.
Design TipConsistent spacing and insulation material give more predictable impedance.
Limit ReminderReal cable twisting pitch, insulation shape, shielding, and nearby metal can change measured impedance.
Tip: If you are designing for a strict impedance target such as 100 Ω differential, verify the final cable or PCB pair with measurement. This calculator is best for geometry-level planning and quick comparison.
Frequently Asked Questions
What is twisted-pair impedance?
Twisted-pair impedance is the characteristic impedance formed by two nearby insulated conductors. It depends mainly on spacing, wire diameter, and dielectric constant.
Why does dielectric constant affect impedance?
A higher dielectric constant increases capacitance between the wires. This usually lowers characteristic impedance and increases signal delay.
What does Zo mean?
Zo means characteristic impedance. It is the impedance a signal sees when traveling along a long uniform cable or transmission line.
Does twisting pitch affect the result?
Yes. Real twisted-pair cable pitch can affect measured impedance, especially at higher frequencies. This calculator uses a simplified geometry-based estimate.
Can I use this for Ethernet cable?
It can help explain the geometry effect, but commercial Ethernet cable should be tested against cable standards because insulation, twist rate, shielding, and manufacturing tolerance matter.
What unit is delay shown in?
Delay is shown in nanoseconds per inch, which is useful for estimating timing effects over short cable lengths.
Why do spacing and diameter matter?
Spacing changes electric and magnetic field distribution between the wires, while diameter changes conductor geometry. Together they strongly affect impedance.
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