What is a bubble chart?

A bubble chart is a scatter plot where marker size carries a third variable, so a single point communicates three numbers at once:

• x axis = metric 1
• y axis = metric 2
• bubble size = metric 3 (volume/magnitude)

Add colorcolor and you’re encoding a fourth variable too — which is exactly what px.scatter(..., size=...)px.scatter(..., size=...) gives you; a bubble chart isn’t a separate chart type in Plotly, it’s a scatter plot with the sizesize argument filled in.

Example

import pandas as pd
import plotly.express as px
 
df = pd.DataFrame({
    "city": ["Pune", "Delhi", "Mumbai", "Bengaluru"],
    "sales": [120, 180, 90, 160],
    "profit": [30, 45, 10, 35],
    "orders": [200, 350, 120, 280],
})
 
fig = px.scatter(
    df,
    x="sales",
    y="profit",
    size="orders",
    color="city",
    hover_name="city",
    title="Sales vs Profit (bubble size = orders)",
)
fig.show()

import pandas as pd
import plotly.express as px
 
df = pd.DataFrame({
    "city": ["Pune", "Delhi", "Mumbai", "Bengaluru"],
    "sales": [120, 180, 90, 160],
    "profit": [30, 45, 10, 35],
    "orders": [200, 350, 120, 280],
})
 
fig = px.scatter(
    df,
    x="sales",
    y="profit",
    size="orders",
    color="city",
    hover_name="city",
    title="Sales vs Profit (bubble size = orders)",
)
fig.show()

Plotly scales bubble area (not raw radius) to the sizesize column by default, which is the perceptually correct choice — doubling a value should roughly double the visual area, not the diameter.

Tips

• Keep sizes reasonable; very large bubbles hide others — cap the biggest bubble at a sensible max area.
• Use hover tooltips (hover_namehover_name) to reduce label clutter instead of printing every city name on the chart.
• Watch out for overlap: when bubbles are close together, consider adding opacityopacity so overlapping regions stay readable.

  flowchart LR
  A["px.scatter(x, y)"] --> B["+ size=column
marker area encodes metric 3"]
  B --> C["+ color=column
hue encodes metric 4 (category)"]
  C --> D["Bubble chart:
4 variables, 1 point per row"]

Next

Continue to: Sunburst Charts for visualizing hierarchical data.

🧪 Try It Yourself

Exercise 1 – Turn a Scatter into a Bubble Chart

Exercise 2 – Reduce Label Clutter with hover_name

Exercise 3 – Add a Fourth Variable with Color