Design Number, Currency, and Unit Formatting

Content & UX Writing · microcopy, internationalization, tables

Updated 2026-07-28

Format for reading, not for storage. A raw value straight from the database is a technical detail that leaks into the interface as a usability problem.
Group thousands. A seven-digit number without separators has to be counted rather than read, and users will misread it by a factor of ten.
Respect local conventions for separators, currency position, and negative values. Swapping a decimal point for a comma changes the meaning of a price by three orders of magnitude.
Always name the currency when more than one is possible. A bare symbol is not enough in a product with several dollar or krone regions.
Keep decimals consistent within a column. Mixed precision makes a table impossible to scan and makes small differences look like large ones.
Align numbers to the right and use tabular figures. Digits of equal width are the difference between a column you can compare and a column you have to read.
Abbreviate only where precision does not matter. Summary tiles can round to thousands, but an invoice line, an account balance, and an export never can.
Attach the unit to the number and keep it visible. A column header that carries the unit stops working the moment the row is copied, exported, or read out.
Be explicit about what zero, empty, and unknown mean. They are three different values and showing them all as a dash hides real information.

Numbers are the part of an interface people act on most literally, so formatting them is a correctness task, not a polish task.