Tone numbers are numerical digits used like letters to mark the tones of a language. The number is usually placed after a romanized syllable. Tone numbers are defined for a particular language, so they have little meaning between languages.
Other means of indicating tone in romanization include diacritics, tone letters, and orthographic changes to the consonants or vowels. For instance, in Mandarin, the syllable 马 (which has a falling-rising tone) is represented in Wade-Giles romanization as ma3, with a tone number; in Hanyu Pinyin as mǎ, with a diacritic; and in Gwoyeu Romatzyh as maa, with a change in the vowel.
In the Chinese tradition, numbers, diacritics, and names are assigned to the historical four tones of Chinese. These are consistent across all Chinese dialects, reflecting the development of tone diachronically. However, it is also common to number the tones of a particular dialect independently of the others. For example, Standard Chinese has four–five tones and the digits 1–5 or 0–4 are assigned to them; Cantonese has 6–9 tones, and the digits from 0 or 1 to 6 or 9 are assigned to them. In this case, Mandarin tone 4 has nothing to do with Cantonese tone 4, as can be seen by comparing the tone charts of Standard Chinese (Mandarin), Cantonese, and Taiwanese Hokkien.
|Tone name||dark level||light level||rising||departing||neutral|
|Tone letter||˥||˧˥||˩, ˨˩˦||˥˩||(none)|
|Tone number||1||2||3||4||5||6||7 (1)||8 (3)||9 (6)|
|Tone name||dark level||dark rising||dark departing||light level||light rising||light departing||upper dark entering||lower dark entering||light entering|
|Tone letter||˥, ˥˧||˧˥||˧||˨˩, ˩||˩˧||˨||˥||˧||˨|
|Taiwanese (臺灣話) and Min Nan (閩南語)|
|Tone name||dark level||rising||dark departing||dark entering||light level||not
|light departing||light entering|
Note: Tone sandhi rules and the unstressed syllable of Mandarin are not listed here for simplicity.
To enhance recognition and learning, color has also been associated with the tones. Although there are no formal standards, the de facto standard has been to use red (tone 1), orange (tone 2), green (tone 3), blue (tone 4) and black (tone 5). This color palette has been implemented in translation tools  and online dictionaries
Although such numbers are useless in comparative studies, they are convenient for in-dialect descriptions:
- In Mandarin, the numeral one, originally in tone 1, is pronounced in tone 4 if followed by a classifier in tone 1, 2, or 3. It is pronounced in tone 2 if the classifier has tone 4.
- In Taiwanese tone sandhi, tone 1 is pronounced as tone 7 if followed by another syllable in a polysyllabic word.
For the numbers of the traditional tone classes, which are consistent between dialects, see four tones in Middle Chinese.
- Nathan Dummit, Chinese Through Tone & Color (2008) or www.chinesecoloured.com
- Loqu8 iCE, a popup Chinese-English dictionary and translation tool
- MDBG Chinese-English Dictionary. In Display Options, "Mandarin tone colors", 
- Branner, David Prager (ed.) (2006). The Chinese Rime Tables: Linguistic Philosophy and Historical-Comparative Phonology. Studies in the Theory and History of Linguistic Science, Series IV: Current Issues in Linguistic Theory; 271. Amsterdam: John Benjamins. ISBN 90-272-4785-4.
- Uy, Dr. Tim and Jim Hsia (ed.) (2009). Webster's Digital Chinese Dictionary: Advanced Reference Edition. California: Loqu8 Press.