ggplot2 ylab() in R: Set the Y Axis Label

The ylab() function in ggplot2 sets the y axis label of a plot in a single short call. It is the single-axis shortcut for labs(y = ...), useful when only the y axis title needs to change and every other label should be left alone.

ylab("Miles per gallon")                             # set the y axis label
ylab(NULL)                                           # remove the y axis label
ylab("")                                             # keep slot, blank text
ylab("Fuel economy\n(miles per gallon)")             # multi-line y label
ylab(expression(MPG~(mu*g/L)))                       # math expression label
p + ylab("MPG") + theme(axis.title.y = element_text(face = "bold"))   # bold
labs(y = "Miles per gallon")                         # the long form

What ylab() does in one sentence

ylab() writes the y axis title slot of a ggplot2 plot, and only that slot. Every other label (x axis, plot title, subtitle, caption, tag, legend) needs xlab(), ggtitle(), or labs() to set it.

It is a thin wrapper around labs(y = ...). The two calls ylab("MPG") and labs(y = "MPG") produce identical output. Reach for ylab() when the y axis label is the only thing changing on the plot, because the call reads as a single intent.

Syntax

ylab(label). The single argument is the text shown to the left of the y axis. Pass a character string, NULL to remove the label, or an expression() for math notation.

The base plot p is reused across the next examples, so each block isolates the y-label change.

Six common ylab() patterns

1. Set a basic label

2. Label with units in parentheses

3. Remove the y axis label

NULL removes the slot and the plot reclaims the horizontal space to the left of the axis. An empty string (ylab("")) keeps the slot blank, leaving a gap.

4. Multi-line label via newline

A \n inside the string forces a line break. Wrapping the y label is more common than wrapping the x label, because vertical text on the left side has limited horizontal room before it starts crowding the plot.

5. Math notation via expression()

expression() accepts R's plotmath syntax. Use ~ for spaces, ^ for superscripts, [] for subscripts, and Greek names like mu, sigma, or theta for symbols. Run ?plotmath for the full grammar.

6. ylab() works for discrete y axes too

There is no separate function for discrete axes. ylab() writes whatever the y axis is, continuous or discrete, log-scaled or linear.

ylab() vs labs() vs xlab() vs ggtitle()

ylab() is the single-axis shortcut; labs() covers every slot at once. Pick ylab() when only the y label is changing, and labs() when the x label, plot title, or any other slot also needs an update.

Under the hood, every shortcut calls labs(). Mixing them in one plot works (each writes its own slot), but a single labs() call is easier to maintain than four scattered calls. See the official ggplot2 reference for labs().

Common pitfalls

Pitfall 1: confusing the label with the tick numbers. ylab() controls the title to the left of the axis, not the numbers along it. To reformat the tick numbers (commas, percents, dollars), use scale_y_continuous(labels = scales::comma) or scales::percent.

Pitfall 2: ylab("") leaves a blank gap. An empty string keeps the slot and reserves horizontal space. Use NULL (ylab(NULL)) to remove the slot completely and let the plot reclaim the room.

Pitfall 3: setting the label inside aes(). Writing aes(y = mpg) only maps the column; it does not set the label. The label defaults to the column name ("mpg"), and you override it with ylab("Miles per gallon") or labs(y = ...).

Pitfall 4: forgetting that coord_flip() swaps the axes. After coord_flip(), the y axis appears horizontally at the bottom, but ylab() still writes the original y slot. The label moves with the axis. Use labs(x = ..., y = ...) if the swap confuses readers, since the slot meaning is unchanged but the visual position is not.

Pitfall 5: ylab() does not label a secondary axis. A right-side secondary y axis is set by scale_y_continuous(sec.axis = sec_axis(~ ., name = "Right label")). Calling ylab() only writes the primary (left) y axis.

Try it yourself

Related ggplot2 functions

After mastering ylab(), look at:

• xlab(): the x axis equivalent
• labs(): set every label (x, y, title, subtitle, caption, tag, legend) in one call
• ggtitle(): the plot title shortcut
• theme(): control font size, color, weight, and angle of axis titles and tick text
• scale_y_continuous(name = ...): an alternative way to set the y label that also lets you control breaks, limits, and tick formatting in the same call

FAQ

How do I change the y axis label in ggplot2?

Use ylab("Your label") and add it to the plot with +. For example, ggplot(mtcars, aes(wt, mpg)) + geom_point() + ylab("Miles per gallon") renders a scatter plot with "Miles per gallon" to the left of the y axis. The labs(y = "Miles per gallon") form is equivalent and is preferred when the x label or plot title is being set in the same call.

What is the difference between ylab() and labs() in ggplot2?

ylab() sets only the y axis label; labs() sets every label on the plot, including x axis, title, subtitle, caption, tag, and legend titles. Both produce identical output when only the y slot is involved, because ylab() is defined as a thin wrapper around labs(y = ...). Use ylab() for single-axis tweaks and labs() when several slots change in one call.

How do I remove the y axis label in ggplot2?

Pass NULL: ylab(NULL). This removes the label slot completely and the plot reclaims the horizontal space to the left of the axis. Passing an empty string (ylab("")) is different: it keeps an empty slot beside the axis, leaving a visible gap that usually looks like a layout bug. Use NULL to drop the label, and "" only when the gap is wanted as a spacer.

How do I rotate or change the font of the y axis label in ggplot2?

ylab() only writes text. Styling lives in theme(). Add theme(axis.title.y = element_text(face = "bold", color = "navy", size = 12, angle = 90)). The default y label is rotated 90 degrees so it reads bottom-to-top; pass angle = 0 to make it horizontal, which is more readable but consumes more horizontal space. Tick numbers along the y axis are styled separately with theme(axis.text.y = ...).

Can I use math notation or Greek letters in ylab()?

Yes. Pass an expression() instead of a string: ylab(expression(mu[y]~(mg/dL))) renders as a Greek mu with a subscript y followed by "(mg/dL)". Use ~ for spaces, ^ for superscripts, [] for subscripts, and Greek names like mu, sigma, theta for symbols. Run ?plotmath for the full grammar.