Weekday Abbreviations: One-, Two-, and Three-Letter Codes Across Languages
Last reviewed on 2026-05-09
Open a weekly planner, a flight schedule, or a German bus timetable, and you'll quickly see that languages don't agree on how to abbreviate the days of the week. English diaries often use single letters — S M T W T F S. German timetables prefer two-letter forms — Mo Di Mi Do Fr Sa So. Software working with international dates uses three-letter forms in English (Mon, Tue, …) or numeric ISO codes. This page is a working reference for the abbreviations you're most likely to meet, why they look the way they do, and where they can trip you up.
Why English single-letter codes fail and two-letter codes don't
If you write a row of single letters for the seven English weekdays, you get S M T W T F S — two pairs that collide. Sunday and Saturday both start with S; Tuesday and Thursday both start with T. The convention solves the ambiguity contextually: in a horizontal weekly planner, the first S is whichever day starts your week (Sunday in US-published planners, Monday-first planners drop the leading Sunday), and the second always means the other one. The same logic applies to T.
Two-letter codes resolve the collision: Su Mo Tu We Th Fr Sa. Three-letter codes resolve it again with redundancy: Sun Mon Tue Wed Thu Fri Sat. Most software libraries and spreadsheet locales standardise on the three-letter form because it is unambiguous, fits in narrow columns, and lines up across rows.
Side-by-side abbreviations across languages
| Language | Mon | Tue | Wed | Thu | Fri | Sat | Sun |
|---|---|---|---|---|---|---|---|
| English (3-letter) | Mon | Tue | Wed | Thu | Fri | Sat | Sun |
| English (2-letter) | Mo | Tu | We | Th | Fr | Sa | Su |
| Spanish | lun | mar | mié | jue | vie | sáb | dom |
| French | lun | mar | mer | jeu | ven | sam | dim |
| Italian | lun | mar | mer | gio | ven | sab | dom |
| German (2-letter) | Mo | Di | Mi | Do | Fr | Sa | So |
| Dutch | ma | di | wo | do | vr | za | zo |
| Swedish | mån | tis | ons | tor | fre | lör | sön |
| Polish | pn | wt | śr | cz | pt | sob | nd |
| Russian | пн | вт | ср | чт | пт | сб | вс |
| Greek | Δευ | Τρι | Τετ | Πεμ | Παρ | Σαβ | Κυρ |
| Japanese (single char) | 月 | 火 | 水 | 木 | 金 | 土 | 日 |
| Chinese (single char) | 一 | 二 | 三 | 四 | 五 | 六 | 日 |
For complete day names, pronunciations, and grammar notes, see the language hubs: Spanish, French, Italian, German, Dutch, Swedish, Polish, Russian, Greek, Japanese, and Chinese.
Patterns to notice
Three-letter Romance languages
Spanish, French, and Italian all use three-letter abbreviations that drop the suffix and keep the recognisable beginning of each name. Spanish keeps the accent on mié and sáb; French and Italian drop their accents in this short form. Software locales sometimes silently strip accents in tight column widths, so the displayed form may be mie or sab on some calendars.
Two-letter Germanic and Slavic languages
German has standardised on two letters because three-letter abbreviations would collide for several days that begin with the same syllable. Polish takes the same approach with even tighter abbreviations (pn for poniedziałek). Dutch follows the German pattern but in lower case. Russian uses two-letter Cyrillic codes that are common on calendars and timetables.
Single-character East Asian forms
Japanese and Mandarin both use a single character per day, but their underlying systems differ. Japanese uses element-based names — Moon, Fire, Water, Wood, Metal, Earth, Sun — and abbreviates each to its element character (月火水木金土日). Chinese uses a numbered system: xīngqī yī (week one = Monday) through xīngqī liù (week six = Saturday), with xīngqī rì or xīngqī tiān for Sunday. The single-character abbreviation is just the number — 一 for Monday, 二 for Tuesday, and so on. See numbered vs. named day systems for the broader pattern.
ISO codes for software
When you need an unambiguous numeric code rather than a letter abbreviation, ISO 8601 defines:
- Monday = 1
- Tuesday = 2
- Wednesday = 3
- Thursday = 4
- Friday = 5
- Saturday = 6
- Sunday = 7
This is the convention returned by strftime's %u directive in C-derived languages and by the ISOWEEKDAY function in Excel and Google Sheets. Be careful: the older %w directive returns Sunday = 0 through Saturday = 6, and the original WEEKDAY function defaults to Sunday = 1 through Saturday = 7. A spreadsheet that mixes the two conventions in the same workbook is a frequent source of off-by-one calendar bugs.
A short checklist for picking an abbreviation
- For a printed weekly planner. Pick the language's standard letter form (one letter for English with the SS/TT context, two letters for German/Dutch, three for Romance languages).
- For a multilingual UI. Use locale-aware libraries — they already store the conventional abbreviation for each language and adjust accent handling automatically. Don't hardcode English abbreviations and translate them.
- For a database column. Store the ISO numeric code (1 = Monday) rather than the abbreviation. Display layers can format it however the user's locale requires.
- For a public timetable. Match the convention of the country you're publishing in. Travellers expect to see the local form.
Common pitfalls
A few mistakes show up repeatedly in published material:
- Using English three-letter forms in a non-English calendar. A diary that says "Mon Tue Wed" in a Spanish-language product looks careless even when accurate, because Spanish readers expect
lun mar mié. - Mixing two- and three-letter forms in the same column. Pick one width and stick with it.
- Stripping accents. Accents change letter identity in many languages. Where they are part of the standard abbreviation (Spanish
mié,sáb; Polishśr), keeping them is the correct choice unless your medium genuinely cannot render them. - Confusing ISO and locale week numbering. When abbreviations sit alongside week numbers, the same Tuesday in early January can fall in different week numbers depending on which system is in force. See first day of the week by country.