Draw Bode plots online
Engineering Plots is a free online Bode plot generator. Enter a transfer function H(s) = N(s) / D(s) and it instantly draws the magnitude and phase frequency response, with gain and phase margins and crossover frequencies marked for you.
What is a Bode plot?
A Bode plot describes the steady-state response of a linear, time-invariant system to sinusoidal inputs of different frequencies. It is one of the most common tools in control systems and signal processing for seeing how a system shapes a signal.
It consists of two graphs sharing a logarithmic frequency axis: the magnitude plot shows 20·log10|H(jω)| in decibels, and the phase plot shows the angle of H(jω) in degrees. Together they reveal bandwidth, resonance, roll-off, and stability margins at a glance.
How to draw a Bode plot from a transfer function
- Enter the numerator and denominator of your transfer function — as coefficient lists (e.g. 1, 2, 1) or as typed polynomials (e.g. s^2 + 2s + 1).
- Read the magnitude (top) and phase (bottom) plots; the frequency axis is shared and logarithmic.
- Toggle the gain and phase crossover markers to read the gain margin and phase margin directly off the curve.
- Click the curve to pin exact values, cascade a lead/lag compensator, or load a preset to explore.
Frequently asked questions
- What is a Bode plot?
- A Bode plot shows how a linear system responds to sinusoids across frequency. It has two graphs: magnitude in decibels and phase in degrees, both plotted against frequency on a logarithmic scale.
- How do you draw a Bode plot from a transfer function?
- Enter the numerator and denominator of H(s), either as coefficient lists or as typed polynomials. The tool evaluates H(jω) over a range of frequencies and plots 20·log10|H(jω)| for magnitude and the angle of H(jω) for phase.
- What are gain margin and phase margin?
- Gain margin is how much the loop gain can increase before instability, read at the phase crossover (−180°). Phase margin is the extra phase lag tolerable at the gain crossover (0 dB). Both are computed and shown automatically.
- Is this Bode plot generator free?
- Yes. Engineering Plots runs entirely in your browser with no signup, no install, and no cost.