Scaling Down Brackets in LaTeX
If you need smaller brackets in your documents, the most obvious answer is also the one that causes the most headaches. You can just use \left( and \right), but sometimes those brackets come out huge and ruin the layout. I spent an afternoon wrestling with this when someone wanted square brackets half the normal size around a single variable in a fraction. There are three approaches people actually use in practice. The first is using explicit sizing commands. You can write something like \bigl( x \bigr) or \biggl[ a + b \biggr] where the s and l versions give you slightly tighter control. The difference between \bigl and \big matters more than you might expect when you are stacking sizes. These commands give you six discrete sizes: \small, \big, \Big, \bigg, and so on. They are not actually related to font size commands, so don't get those confused.
The second approach is the \smash command, which strips vertical space from content. I used this when dealing with a matrix that had tiny bracket notation around individual elements. By wrapping the bracket portion in \smash, you remove the extra height that LaTeX normally adds. The tradeoff is that adjacent lines can collide, so check your output carefully. I had a case where two fractions in a stack ended up overlapping because I smashed too aggressively. Adding \vphantom{content} to nearby elements fixed it without changing the visual appearance. The third option is the scalerel package, which lets you scale braces to match the height of whatever sits next to them. This is genuinely useful when you have asymmetric expressions inside brackets. It requires loading scalerel in your preamble with \usepackage{scalerel}, then using the \scaleleftright command. Here is a minimal example that works reliably:
\usepackage{braket} allows you to write things like \bra{\psi} and \ket{\phi} with bracket notation that is already sized appropriately for quantum mechanics notation. If you are doing physics or math-heavy documents, this package saves you from reinventing bracket sizing repeatedly. A common mistake people make is trying to manually resize brackets with \resizebox from the graphicx package. This works visually but breaks spacing and line height in ways that are hard to debug later. I have seen entire documents where line spacing went haywire because someone used \resizebox on a bracket that happened to sit on a line with a tall character. The real problem with small brackets is that they do not pair well with tall expressions. If you have a large fraction or integral inside your brackets and you shrink the brackets to fit, the expression inside looks cramped. The alternative here is to let the brackets be large and use the sizing commands rather than trying to force everything into a smaller footprint. A bracket that is clearly too small for its contents is worse than one that is clearly too large, in my experience. Readers notice mismatched sizing instantly and it creates visual noise.
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If you are generating LaTeX from another tool or working with dynamic content, the bracket sizing becomes a real pain because the content changes every time. In those cases, \left and \right remain the only sane default, even if they occasionally overshoot. You can pair them with \bigl and \bigr overrides when needed, but don't try to micro-manage every instance.
