In math mode you place a small mark over a letter to add meaning: \hat for an estimator, \dot for a time derivative, \bar for a mean or conjugate, \vec for a vector. Two things are worth fixing in your mind. Most accents are fixed-width, sized for a single symbol — applied to several letters they do not stretch. And a few have a stretchy counterpart that widens to fit, such as \hat versus \widehat. This page is a quick lookup of math accents: a table of the fixed-width marks, the contrast with the stretchy forms, and how to accent i and j. The deeper material — braces, under-accents, and stacking arbitrary symbols — is left to “Over/under decorations.”
How math accents work
Math accents are written inside math mode as commands that take one letter as their argument, like \hat{x}. Writing one straight into the body (text mode) is an error, or gives a different, text-mode accent, so enter math mode first: $\hat{x}$. The single-letter accents covered here are part of standard LaTeX, as the table below shows — no extra package is needed (only the three- and four-dot \dddot and \ddddot require amsmath).
These marks carry no fixed meaning of their own; they follow the conventions of each field. In physics \dot{x} is a time derivative (the rate of change of x in time); in statistics \hat{\theta} is an estimator of a parameter and \bar{x} a sample mean; for complex numbers \bar{z} denotes the conjugate. In short, this page is about *which* mark to choose; the next page is about how to *stack* them or run them across a whole expression.
Fixed-width accents (lookup)
The table below is the full set of fixed-width accents that sit at the size of a single symbol. They do not stretch over a multi-letter argument; they sit centered over the first symbol. Because this site has no math renderer, the “look” column describes each mark in words (compile locally to see the actual output).
| Command | What it looks like | Typical use |
|---|---|---|
\hat | A caret (^, circumflex) | Estimators, unit vectors |
\tilde | A tilde (~, wave) | Approximations, transformed quantities |
\bar | A short bar (macron) | Means, complex conjugates |
\vec | A small rightward arrow | Vector quantities |
\dot | A single dot | First time derivative |
\ddot | Two dots (dieresis) | Second time derivative |
\dddot | Three dots (needs amsmath) | Third time derivative |
\ddddot | Four dots (needs amsmath) | Fourth time derivative |
\acute | An acute accent (rising stroke ´) | Linguistics; occasionally math |
\grave | A grave accent (falling stroke `) | Linguistics; occasionally math |
\check | A check (háček, v-shape ˇ) | Marks in geometry and algebra |
\breve | A breve (cup shape ˘) | Marks in geometry and algebra |
\mathring | A small ring (˚) | Geometry symbols; occasionally units |
\[
\dot{x}, \quad \ddot{x}, \quad \bar{x}, \quad \hat{p},
\quad \tilde{a}, \quad \vec{v}, \quad \check{s}, \quad \mathring{r}
\]These set, respectively, one and two dots over x, a short bar over x, a small caret over p, a tilde over a, a small rightward arrow over v, a v-shape over s, and a small ring over r. Command names are case-sensitive, and the argument goes in braces (you may drop them for a single letter, as in \hat x, but \hat{x} is the safer, more readable habit).
Fixed vs stretchy counterparts
Several accents have a counterpart that stretches to the width of the argument. Where \hat{x} is a small caret over one letter, \widehat{xyz} spreads a caret across the whole of xyz. The rule of thumb: a stretchy form to cover a whole expression, a fixed-width mark for a single letter. The table pairs them up.
| Fixed (one letter) | Stretchy (whole expression) | Notes |
|---|---|---|
\hat | \widehat | Standard LaTeX; caret widens to fit |
\tilde | \widetilde | Standard LaTeX; tilde widens to fit |
\bar | \overline | Standard LaTeX; line stretches over the contents |
\vec | \overrightarrow | Standard LaTeX; rightward arrow stretches to fit |
\[
\hat{x} \;\text{vs.}\; \widehat{xyz}, \qquad
\bar{z} \;\text{vs.}\; \overline{x + y}, \qquad
\vec{a} \;\text{vs.}\; \overrightarrow{AB}
\]Two cautions. First, in standard LaTeX **only \widehat and \widetilde are truly stretchy accents** (\overline and \overrightarrow are not strictly accents but a line and an arrow laid over the argument — they belong here because they stretch). Second, \widehat and \widetilde pick from a few predrawn sizes, so over a very long expression they may not widen enough and can look awkward; in that case consider \overline.
The command most often misused is \vec. Writing \vec{AB} does not stretch the arrow — it puts a small arrow effectively over B, and does not read as a directed segment from A to B. For an arrow that spans both ends, use \overrightarrow{AB}. For more on the stretchy forms — double-headed arrows, under-side arrows, and so on — see “Over/under decorations.”
Accenting i and j (the dotless forms)
Putting an accent on i or j makes the letter’s own dot collide with the accent, which looks bad. The tradition is therefore to build on the **dotless forms \imath (dotless i) and \jmath (dotless j)**. Writing \hat{\imath}, for example, sets just the caret cleanly over a dotless i. Both are standard math-mode commands; no extra package is required.
\[
\hat{\imath}, \quad \vec{\jmath}, \quad \dot{\imath}
\]Note too that double accents do not stack cleanly. Layering two, as in \hat{\vec{x}}, tends to leave the upper mark floating or off-center. If you merely want more dots, use \ddot or amsmath’s \dddot and \ddddot; for genuinely layered marks, build them explicitly with \overset, covered on the next page.