Typography

House typefaces

Where	Typeface	Notes
Office (Excel, PowerPoint, Word) and BI tools (Power BI)	Calibri, or Aptos to match the Office default	Both are installed on every Windows machine and have the right figures for numbers (see below). Calibri is narrower, so more text fits without shrinking it. BI services show only fonts installed on the reader’s machine, so use Calibri there too.
Web and code (D3, Plotly, ggplot, matplotlib)	IBM Plex Sans	Open source, with many weights. Turn on tabular figures (font-variant-numeric: tabular-nums in CSS).

Use one typeface per visual. Create hierarchy with weight and size, not with a second font.

Sizes and weights

Element	Weight	Relative size	Minimum in print
Title	Bold or semibold	Largest, about 1.5× body	12 pt
Subtitle	Regular	About 1.15× body	10 pt
Labels, axis values, legend	Regular	Body	9 pt
Source, notes	Regular	About 0.85× body	7 pt
Big number value	Bold	As large as the space allows

Use sentence case and left alignment for the title, subtitle, source and note. Don’t use all caps except for short labels, and don’t use italics for emphasis.

Text is horizontal. Rotated text is a last resort, after you’ve tried a horizontal bar chart, fewer labels, and abbreviations.

Choosing a typeface

A typeface for your own guide needs three properties:

Available

Installed on, or easy to install on, every device and tool your team uses.

Legible

Clear at small sizes, on screen and in print. Sans-serif is the safe choice.

Several weights

At least regular and bold, ideally light and semibold too, so you can emphasise the message and de-emphasise supporting text.

And it needs these properties for numbers:

Property	What it means	Why it matters
Lining figures	All digits sit on the baseline at the same height.	Numbers in labels look even.
Tabular figures	All digits are the same width.	Columns of numbers line up.
Multiplexed weights	Digits stay the same width across weights.	Bolding a highlighted label doesn’t shift the layout.

Of the common Windows sans-serifs (Aptos, Arial, Calibri, Segoe UI and Verdana), only Aptos and Calibri meet all three number criteria.

If your brand already has a typeface, check it against these criteria before adopting it for charts. Many display typefaces have old-style or proportional figures, which make tables and axis labels look ragged.

Sans-serif is the safe choice: it is generally more legible at small sizes and on screen, and there is little evidence that serifs read better in print. See Typography research.