Modulation Index Calculator

Switch between envelope, ratio, or deviation inputs. Auto-convert units and show percent modulation instantly too. Download clean summaries with examples, formulas, and guidance included.

Select a modulation family to unlock its methods.
Choose how you want to compute the index.
Used only for AM amplitude entries.
Used for fm and bandwidth inputs.
Used for Δf entry.
Used for peak phase deviation entry.
Formula: m = Vm / Vc
Formula: m = (Vmax − Vmin) / (Vmax + Vmin)
Solve: Vm = m × Vc
Solve: Vc = Vm / m
Formulas: β=Δf/fm, BW≈2(Δf+fm)
Solve: Δf=β×fm, BW≈2(Δf+fm)
Estimate: Δf≈BW/2−fm
Enter degrees or radians, based on your unit choice.
Adds Δf and bandwidth estimate for sinusoidal PM.
Formulas: mp=Δφ(rad), Δf≈mp×fm
Tip: keep units consistent. If you switch units, re-check inputs.

Example Data Table

Case Type Inputs Key result
1 AM Vm=2.0 V, Vc=10.0 V m=0.20 (20%)
2 AM Vmax=12 V, Vmin=8 V m=0.20 (20%)
3 FM Δf=5 kHz, fm=1 kHz β=5.00, BW≈12 kHz
4 FM β=2.5, fm=2 kHz Δf=5 kHz, BW≈14 kHz
5 PM Δφ=45°, fm=1 kHz mp=0.785 rad, Δf≈0.785 kHz
Values are illustrative. Your signal shape may affect bandwidth.

Formula Used

AM (Amplitude Modulation)

  • m = Vm / Vc (ratio of modulating to carrier amplitude)
  • m = (Vmax − Vmin) / (Vmax + Vmin) (envelope method)
  • % modulation = 100 × m

FM (Frequency Modulation)

  • β = Δf / fm (frequency deviation divided by modulating frequency)
  • BW ≈ 2(Δf + fm) (Carson’s bandwidth approximation)

PM (Phase Modulation)

  • mp = Δφ in radians (peak phase deviation)
  • Degrees are converted using rad = deg × π / 180
  • For sinusoidal PM: Δf ≈ mp × fm

How to Use This Calculator

  1. Select the modulation type: AM, FM, or PM.
  2. Pick a method matching what you measured or know.
  3. Set units, then enter your values in the fields.
  4. Press Calculate to view results above the form.
  5. Use Download CSV or Download PDF to save your summary.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.