RFC 3339 vs ISO 8601

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Format Listing

Notes:

• This table is not exhaustive.
• This page targets ISO 8601-1:2019 and ISO 8601-2:2019. Previous editions and drafts contain key differences.
• RFC 3339 allows for other characters to replace T but only gives a space character as an example.
• RFC 3339 and ISO 8601 are both case-insensitive so every T, W, P, R, or Z could be t, w, p, r, or z respectively.
• ISO 8601 allows decimal fractions of the smallest time value. These are represented here by a single fractional digit but the standard allows arbitrary precision.
• ISO 8601 prefers commas to dots for decimal separation but they are interchangeable in all formats.
• ISO 8601 recommends U+2212 MINUS "−" for timezones west of Greenwich. The formatter defaults to U+2D HYPHEN MINUS "-" which is valid under both standards.
• ISO 8601-1:2019 permits omitting the T in the time of day representations (Times) when unambiguous.
  However, a T (or t) is always required for date and time of day representations (Date-Times).
  Previous editions also allowed omitting the T in Date-Times but it was never permitted to insert alternative characters (e.g. space or underscore).
• The format key is given below the table.

Format Key

%L - Millennium
%C - Century
%X - Decade
%Y - Year
%M - Month
%D - Day
%V - Week Year
%W - Week
%w - Week Day
%O - Ordinal Day

%h - Hour
%m - Minute
%s - Second
%u - Microsecond

%Z - Zone Hour including +/-
%z - Zone Minute

%[,.]3x - Value including fraction with given precision, using either comma or dot.
%−Z     - Use U+2212 for negative timezone hours (ISO recommended)

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