Days of the week in Thai: the seven วัน names, RTGS and day colours

Seven planets from Sanskrit: where the Thai day names come from

Every one of the days of the week in Thai is built the same way: วัน (wan), the word Wiktionary glosses as day, daytime and today, plus a planet. The planets are Sanskrit words that reached Thai, according to Wiktionary's etymologies, mostly by way of Old Khmer, where several of them already named the heavenly bodies.

จันทร์ for Monday comes from Sanskrit candra, the shining one, the Moon. อังคาร, Tuesday, goes back to aṅgāra, a heap of glowing charcoal, a fitting name for the red planet Mars. พุธ, Wednesday, is budha, wise or clever, the Indian name of Mercury. The longest name, พฤหัสบดี for Thursday, is Sanskrit bṛhaspati, lord of prayer and the name of Jupiter. ศุกร์, Friday, is śukra, bright or white, for Venus; เสาร์, Saturday, is saura, celestial, for Saturn; and อาทิตย์, Sunday, is āditya, the Sun.

So the Thai week runs on the same seven heavenly bodies as the Latin week behind French lundi or English Saturday, only through an Indian channel. Lao and Khmer, which received the same words from the same source, have close cognates of every name, and Wiktionary lists them under each entry; the days of the week in many languages table sets the three side by side.

Reading the Thai day names: silent letters, tones and RTGS

Learned loanwords keep their Sanskrit spelling, and Thai does not pronounce all of it. จันทร์ is written with ท and ร after the น, yet RTGS gives the word as chan and the IPA as /tɕan/. The mark ์ over the final letters tells the reader to skip them. ศุกร์ and เสาร์ work the same way: suk and sao, with the written ร silent.

Thai has five tones, named in the Wikipedia article on the Thai script as middle, low, falling, high and rising. The seven day names show several of them. วัน and จันทร์ are on the middle tone, พุธ is high, ศุกร์ is low and เสาร์ is rising, as the tone diacritics in the IPA column show. RTGS deliberately leaves tones out, which keeps road signs and maps readable but means that wan sao on a page cannot tell a learner how Saturday sounds.

Thursday deserves a slow reading. The full form วันพฤหัสบดี has six syllables, wan phrue hat sa bo di, and the letter ฤ inside it is a vowel symbol inherited from Sanskrit ṛ. In speech and on signs the word is cut down: CLDR's abbreviated weekday name is พฤหัส, and the site's weekday table records วันพฤหัสฯ, where ฯ, called paiyan noi, marks a formal word shortened by convention.

A colour for every day of the week in Thai tradition

Each day of the week in Thai tradition has a colour, and the Wikipedia article on the Thai solar calendar lists them: yellow or cream for Monday, pink for Tuesday, green for Wednesday, orange for Thursday, light blue for Friday, purple for Saturday and red for Sunday.

The colours follow the same seven heavenly bodies as the names, so the list can be read as a second column of the table above: the Moon is yellow, Mars pink, Mercury green, Jupiter orange, Venus light blue, Saturn purple and the Sun red. Wednesday is the only day whose colour is a plain secondary colour of the painter's wheel, and Monday the only one with two accepted shades, yellow or cream. A learner who memorises the seven names together with their colours gets two cues for each day instead of one.

Using the days of the week in Thai sentences

Thai grammar makes the days of the week in Thai easy to use. Nouns do not change, there are no articles, and no preposition is needed for on: a day name placed in the sentence is enough. ร้านปิดวันอาทิตย์ simply strings shop, close and Sunday together and means the shop is closed on Sundays.

The question what day is it today is วันนี้วันอะไร, literally day-this day-what, and the answer repeats the frame with the day in place of the question word: วันนี้วันพุธ, today is Wednesday. Because วัน already opens every day name, a sentence about days can contain the syllable wan three or four times, and speakers often drop it before the planet when the context is clear.

On paper Thai writes the day first in a full date. The CLDR full date pattern for the Thai locale is the weekday, then ที่ (thi, the ordinal marker), the day of the month, the month name and the year of the Buddhist Era. Wednesday 28 October 2026 therefore becomes วันพุธที่ 28 ตุลาคม พุทธศักราช 2569, and the months in Thai page explains the year.

Where the Thai week starts, and the abbreviations on a calendar

The Unicode CLDR week data, which phones and computers use to lay out calendars, sets Sunday as the first day of the week for Thailand, with Saturday and Sunday as the weekend. A Thai wall calendar therefore usually opens on อา. and ends on ส.

CLDR gives three sets of short names. The abbreviated set drops วัน and keeps the planet, so อาทิตย์, จันทร์, พฤหัส. The short set reduces each to an initial with a full stop: อา. จ. อ. พ. พฤ. ศ. ส. The narrow set is the same without the stops. Sunday and Thursday keep two letters because a single อ would clash with Tuesday and a single พ with Wednesday.