Calculator Inputs
Formula Used
Inductor quality factor compares stored reactive energy to dissipated loss at a given frequency.
- Angular frequency:
ω = 2πf - Inductive reactance:
XL = ωL - Series-loss model:
Q = XL / Rs - Parallel-loss model:
Q = Rp / XL - Resistance for target Q:
Rs = XL / QandRp = Q·XL - Model conversion (at same f):
Rp ≈ XL2/RsandRs ≈ XL2/Rp
Note: Measured losses can include winding resistance, skin effect, proximity effect, and core losses.
How to Use This Calculator
- Enter inductance and pick the correct unit.
- Enter the frequency where you evaluate the inductor.
- Select a resistance model: series loss (Rs) or parallel loss (Rp).
- Choose an operation: compute Q, or solve resistance for a target Q.
- Press Calculate to show results above the form.
- Use CSV or PDF exports to save your outputs.
Example Data Table
| Frequency | Inductance | Model | Loss Resistance | XL (Ω) | Q |
|---|---|---|---|---|---|
| 1 MHz | 10 µH | Series | 0.20 Ω | 62.83 | 314.16 |
| 5 MHz | 4.7 µH | Series | 0.35 Ω | 147.65 | 421.85 |
| 10 MHz | 1 µH | Series | 0.50 Ω | 62.83 | 125.66 |
| 2 MHz | 22 µH | Parallel | 25 kΩ | 276.46 | 90.42 |
| 500 kHz | 100 µH | Parallel | 50 kΩ | 314.16 | 159.15 |
Values are illustrative and vary by construction and frequency.
Inductor Q Factor Guide
1) Meaning of Q in an inductor
The quality factor (Q) describes how efficiently an inductor stores energy compared with how much it loses as heat. A higher Q means lower dissipation for the same reactance, which matters for tuned circuits, filters, and impedance matching.
2) Core equation behind this calculator
At a test frequency f, the inductive reactance is XL = 2πfL. In a series-loss model, Q equals XL/Rs. In a parallel-loss model, Q equals Rp/XL. These forms are equivalent when converted at the same frequency.
3) Typical Q ranges in practice
Q varies widely with construction and frequency. Small ferrite inductors used for power conversion may show Q values around 10–60 at their test frequency, while air‑core RF coils and high‑Q molded inductors can reach roughly 50–300 in favorable bands. Treat these as design starting points, then validate with measurement.
4) Frequency dependence and AC resistance
As frequency rises, effective resistance often increases because of skin effect and proximity effect. That raises Rs, reducing Q even if L stays similar. Leads, solder joints, and PCB copper also add loss at MHz and above, so measurement fixtures matter.
5) Parasitics and self‑resonant frequency
Real inductors include parasitic capacitance. Near the self‑resonant frequency (SRF), the impedance stops behaving like a pure inductor and Q can collapse. For accurate work, evaluate Q well below SRF and include any series capacitors or matching networks separately.
6) Series vs parallel loss models
The series model is common for representing copper loss and many impedance‑analyzer readings. The parallel model is useful when loss appears as a shunt path, especially in high‑impedance resonant tanks. This calculator reports both Rs and Rp equivalents so you can compare datasheets consistently.
7) Design impact on bandwidth and selectivity
In resonant circuits, Q links directly to bandwidth: BW ≈ f0/Q. For example, a 10 MHz tuned stage with Q = 100 has an approximate 100 kHz bandwidth. Higher Q improves selectivity but can increase sensitivity to component tolerances and temperature drift.
8) Practical ways to improve Q
Reduce resistive loss with thicker wire, shorter leads, and low‑loss terminations. Consider Litz wire at lower RF, and optimize turn spacing to reduce proximity loss. Core choice matters: lower‑loss materials and appropriate flux density improve Q at your operating frequency.
FAQs
1) What inputs do I need to calculate Q?
Provide inductance, frequency, and a loss resistance value. Choose whether the resistance is modeled in series (Rs) or in parallel (Rp). The tool converts units and computes Q with the matching formula.
2) When should I use the series resistance model?
Use the series model when losses are primarily copper or winding resistance and your instrument reports series parameters. It is also convenient for estimating Q from measured ESR at a specific frequency.
3) When is the parallel resistance model better?
Use the parallel model for high‑impedance resonant tanks or when a datasheet specifies parallel loss resistance. It can be more intuitive when losses act like a shunt path across the inductor.
4) Why does Q usually drop at higher frequency?
AC resistance increases with frequency due to skin and proximity effects. Core losses can also rise with frequency and flux density. Both mechanisms increase dissipation, lowering Q even if inductance remains similar.
5) Can I solve for the resistance needed to hit a target Q?
Yes. Select “Compute resistance for target Q,” enter the target Q, and choose series or parallel model. The calculator outputs the required Rs or Rp at your chosen frequency.
6) Is Q the same as efficiency?
Not exactly. Q compares reactive energy storage to loss per cycle at a frequency. It correlates with lower loss, but overall circuit efficiency also depends on load, matching, waveform, and other component losses.
7) How should I use the CSV and PDF exports?
Exports capture the computed Q, reactance, and equivalent resistances for documentation. Use CSV for spreadsheets and test logs, and PDF for reports, build notes, or sharing design checks with collaborators.