Equation numbering in LaTeX

An equation with its number on the right is written with the equation environment. Give it a \label and refer to it in the text with \eqref, which adds the parentheses for you. The number updates automatically when you add an equation earlier in the document.

\begin{equation}
  T = 2\pi \sqrt{\frac{L}{g}} \label{eq:period}
\end{equation}

From equation \eqref{eq:period} we determine the gravitational acceleration.

Common mistakes

• Typing the number by hand, e.g. "(3)": once you add an equation, every reference is off.
• "??" in the PDF: the document has to be compiled twice for references to resolve.

See also

• Cross-references in LaTeX
• Aligned equations in LaTeX
• Figure in LaTeX