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To show horizontal grid lines in Matplotlib, call ax.grid(axis="y") on your Axes object. To control whether those lines sit behind or in front of your bars, areas and lines, call ax.set_axisbelow() with True, "line" or False. The combined pattern below handles both steps:
ax.grid(visible=True, axis="y", which="major",
color="0.8", linestyle="--", linewidth=0.8)
ax.set_axisbelow(True)The rest of this guide explains each argument, the three layering modes, and how to fix the most common cases where gridlines do not appear the way you expect.
Draw only horizontal gridlines with axis="y"
Horizontal gridlines are the gridlines that run across the y-axis, so you select them with the axis argument of Axes.grid. Passing axis="y" restricts the grid to that axis, which leaves vertical lines off the chart. The Axes.grid reference documents the full signature.
import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1, 2, 3, 4], [3, 7, 5, 9])
ax.grid(axis="y")
plt.show()The three values accepted by axis are "x", "y" and "both". Use "y" for horizontal lines only, "x" for vertical lines only, or "both" for a full grid.
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Choose which tick group gets gridlines
The which argument decides whether gridlines follow major ticks, minor ticks or both. The three options are:
| Value | Gridlines drawn at | What you need |
|---|---|---|
"major" |
Major tick positions only | Nothing extra; this is the default in the configuration reference |
"minor" |
Minor tick positions only | Minor ticks must exist, or nothing is drawn |
"both" |
Major and minor tick positions | Minor ticks must exist for the minor lines to appear |
If you request minor gridlines on a plot without minor ticks, call ax.minorticks_on() first. Minor gridlines are usually lighter than major ones, so pair them with a lower-contrast color such as "0.9".
ax.minorticks_on()
ax.grid(axis="y", which="both", color="0.9", linewidth=0.5)
ax.grid(axis="y", which="major", color="0.7", linewidth=0.9)Style the horizontal gridlines
Gridlines accept Line2D properties, so the familiar line settings work here. The three you will use most are:
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color: a name, a hex value or a grey level string such as"0.8". Lighter values keep the grid from competing with the data.linestyle: for example"--"for dashed or":"for dotted.linewidth: a value in points. Values near0.5to1.0suit most charts.
These properties are passed directly to ax.grid() as keyword arguments, as shown in the opening example.
Decide whether gridlines sit above or below the data
Axes.set_axisbelow controls the drawing order of the axis, which includes its ticks and gridlines. The reference page opens with the sentence: “Set whether axis ticks and gridlines are above or below most artists.” (Axes.set_axisbelow reference, Matplotlib 3.10.0).
Because ticks and gridlines move together, set_axisbelow is a layering switch for the whole axis, not a setting for one gridline at a time. It accepts three values:
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| Value | Z-order | Relative to patches (bars, spans, filled areas) | Relative to lines and markers |
|---|---|---|---|
True |
0.5 | Below | Below |
"line" |
1.5 | Above | Below |
False |
2.5 | Above | Above |
The default is "line". Patches have a default z-order of 1 and lines have a default z-order of 2, so with the default setting a bar chart shows its gridlines over the bars. That is often why people search for a way to put grid lines behind a plot.
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import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.bar(["Jan", "Feb", "Mar", "Apr"], [120, 95, 140, 110], color="steelblue")
ax.grid(axis="y", color="0.85")
ax.set_axisbelow(True) # gridlines now sit behind the bars
plt.show()Without the set_axisbelow(True) line, the gridlines cross the blue bars. With it, the bars hide the grid where they overlap.
Bring gridlines in front of everything
ax.set_axisbelow(False)Use this when the grid should stay visible over both filled areas and plotted lines, for example as a reference scale on a dense chart. Keep the grid light so it does not hide data.
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Keep gridlines above fills but below lines
ax.set_axisbelow("line")This is the default. It suits most line charts with light filled areas, because the fills stay clean while the lines and markers stay on top.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Set the behaviour for every plot with rcParams
If you want the same grid settings across a notebook or script, set matplotlib’s runtime configuration (rcParams) before you create figures. The configuration reference lists the keys. The grid-related defaults are:
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import matplotlib.pyplot as plt
plt.rcParams["axes.grid"] = True
plt.rcParams["axes.grid.axis"] = "y"
plt.rcParams["axes.grid.which"] = "major"
plt.rcParams["axes.axisbelow"] = TrueSet these values before you call plt.subplots(). Changing them afterwards does not restyle Axes that already exist.
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Check your Matplotlib version
The reference pages above are versioned. The stable Axes.grid page and the Axes API index reflect Matplotlib 3.11.2, while the set_axisbelow page linked here is the 3.10.0 version. For a version-specific answer, check your installed release with import matplotlib; print(matplotlib.__version__) and read the matching documentation.
Troubleshooting common gridline problems
- No gridlines appear. Confirm that
ax.grid(axis="y")runs after your plotting calls, and that no later call turns the grid off. Checkaxes.gridin your rcParams if you expect the grid by default. - Gridlines cross bars or filled areas. Call
ax.set_axisbelow(True). This is the default-behaviour fix shown in the bar chart example. - Gridlines are hidden behind lines or markers you want to see over them. Use
ax.set_axisbelow(True)or keep the default"line"mode, which places lines and markers above the grid. - Minor gridlines do not show. The plot has no minor ticks. Call
ax.minorticks_on()before settingwhich="minor"orwhich="both". - Changing the grid on one Axes affects another. Check whether you set
rcParamsglobally. Settings made throughax.grid()apply only to that Axes.
When the three layering modes are not enough, the Axes API index is the place to look for lower-level control of the axis z-order.
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