ggplot2, change title size

Question

I would like to have my main title and axis title have the same font size as the annotated text in my plot.

i used theme_get() and found that text size is 12, so I did that in my theme statement - this did not work. I also tried to send the relative size to 1, and this did not work

I was hoping someone could please help me.

Code is below

library(ggplot2)
library(gridExtra)  #to set up plot grid
library(stringr)  #string formatting functions
library(plyr)  #rbind.fill function
library(reshape2)  #transformation of tables

dat<-data.frame(
est=c(2.75,2.95,2.86,2.99),
ucl=c(2.92,3.23,3.38,4.91),
lcl=c(2.24,1.67,2.44,1.82),
ord=c(1,2,1,2)
)
dat$varname<-c('Estimate','Predictive','Estimate','Predictive')
dat$grp<-c('Cobalt','Cobalt','Chromium','Chromium')

for (i in unique(dat$grp)) {
  dat <- rbind.fill(dat, data.frame(grp = i, ord=0,
                                    stringsAsFactors = F))
}

dat$grp_combo <- factor(paste(dat$grp, dat$ord, sep = ", "))
dat$grpN <- as.numeric(dat$grp_combo)



rng <- c(0,6)
scale.rng <-1


xstart=-(max(dat$grpN)+2)
xend=4


ThemeMain<-theme(legend.position = "none", plot.margin = unit(c(0,0,0, 0), "npc"), 
                 panel.margin = unit(c(0,0, 0, 0), "npc"), 
                 title =element_text(size=12, face='bold'),
                 axis.text.y = element_blank(), 
                 axis.text.x = element_text(color='black'),
                 axis.ticks.y = element_blank(),
                 axis.title.x = element_text(size=12,color='black',face='bold')
                 )
BlankSettings <- theme(legend.position = "none", 
                       title =element_text(size=12, face='bold'),
                       plot.margin = unit(c(0,0, 0, 0), "npc"), 
                       panel.margin = unit(c(0,0, 0, 0), "npc"),              
                       axis.text.x = element_text(color='white'),                             
                       axis.text.y = element_blank(), 
                       axis.ticks.x = element_line(color = "white"),
                       axis.ticks.y=element_blank(),
                       axis.title.x = element_text(size=12,color='white',face='bold'),
                       panel.grid = element_blank(),panel.grid.major = element_blank(),panel.background = element_blank()
                       )

pd <- position_dodge(width = 0.7)

#######################################################################################################
#MAIN PLOT
#######################################################################################################
mainPart<-
  ggplot(dat, aes(x=-grpN,y=est, ymin=lcl, ymax=ucl, group=1)) +
  scale_y_continuous(name=NULL, breaks=seq(rng[1], rng[2], scale.rng), limits=c(rng[1], rng[2]), expand=c(0,0)) + 
  ylab('Ion Concentration') +
  ggtitle('Mean with 95% HDI')+
  #geom_segment(aes(x=xstart, xend=0, y=0, yend=0), linetype=3, alpha=0.01) +
  geom_linerange(aes(linetype="1"),position=pd) +
  geom_point(aes(shape="1"), fill="white",position=pd) +
  coord_flip() +
  scale_x_continuous(limits=c(xstart,xend), expand=c(0,0))+xlab(NULL)+
  ThemeMain

#######################################################################################################
#varnameS
#######################################################################################################
# ystart & yend are arbitrary. [0, 1] is
# convinient for setting relative coordinates of
# columns
ystart = 0
yend = 1
p1 <- 
  ggplot(dat, aes(x = -varnameN, y = 0)) + 
  coord_flip() + 
  scale_y_continuous(limits = c(ystart, yend)) + 
  BlankSettings+
  scale_x_continuous(limits = c(xstart, xend), expand = c(0, 0)) + 
  xlab(NULL) + 
  ylab('') +
  ggtitle('')

studyList<-
  p1 + 
  with(unique(dat[is.na(dat$varname),c("grpN","grp")]), annotate("text",label=grp, x=-grpN,y=0, fontface='bold', hjust=0)) + #Variable Group varnames
  with(dat[!is.na(dat$var),],annotate("text",label=varname,x=-grpN,y=0.04, hjust=0))  #Variables

#######################################################################################################
#EFFECTS
#######################################################################################################
f<-function(x) round(x,2)
dat$msmt<-paste(f(dat$est),' [',f(dat$lcl),', ',f(dat$ucl),']',sep='')


effectSizes<-p1+
  annotate("text",x=-dat$grpN, y=0.25,label=ifelse(is.na(dat$varname)==T,'',dat$msmt))



grid.arrange(ggplotGrob(studyList), ggplotGrob(mainPart), 
             ggplotGrob(effectSizes), ncol = 3, widths = unit(c(0.19, 
                                                                 0.4, 0.41), "npc"))

Answer 1

+ theme(plot.title = element_text(size=22))

Here is the full set of things you can change in element_text:

element_text(family = NULL, face = NULL, colour = NULL, size = NULL,
  hjust = NULL, vjust = NULL, angle = NULL, lineheight = NULL,
  color = NULL)

Answer 2

Using the theme with plot.title is the easiest way. But there is another option using ggtext which provides Markdown (element_markdown) and HTML rendering for ggplot2. So you can use HTML tags to change the "font-size" of the title for example. The advantage of this is that you can change parts of title easily, so you can give certain parts of the title a different font-size or colors using HTML tags.

Here is a reproducible example:

library(ggplot2)
library(ggtext)
# font size using html
ggplot(mtcars, aes(x = cyl)) +
  geom_bar() +
  ggtitle("<span style='font-size: 22pt;'>This is bigger text</font>") +
  theme(plot.title = element_markdown())

# Change parts of title font size 
ggplot(mtcars, aes(x = cyl)) +
  geom_bar() +
  ggtitle("<span style='font-size: 22pt;'>This is bigger text,</font>
          <span style='font-size: 10pt;'>This is smaller text.</font>") +
  theme(plot.title = element_markdown())

^{Created on 2022-08-24 with reprex v2.0.2}

As you can see, the title has two different font-sizes. For extra information and examples you can check the link above.