The following table shows the syllables of Mandarin Chinese in the combinations of initial and final sounds and as spelled in Hanyu Pinyin. The column headers are Pinyin consonant initials and row headers are Pinyin vowels(vowel combinations). If there is a space in a cell, that means the corresponding consonant and vowel can not make a legal Pinyin.

Notes:

⁂ Represents a zero initial (i.e. where nothing comes before the final sound in the far left column)
* Whenever u comes at the beginning of a syllable, it is written w. W, however, must not appear without an additional vowel, so u as a complete syllable is not written as w by itself but as wu.
†The i in zi, ci, si is different from most other uses of i in that it is short, not long.
‡ The i in zhi, chi, shi, ri is different from most other uses of i in that it is short, not long.
+ Whenever i comes at the beginning of a syllable, it is written y. Thus, Y, however, must not appear without an additional vowel, so not y, yn, yng but yi, yin, ying.
※ Hanyu Pinyin simplifies the spellings of syllables with ü by using the u form instead in cases where no ambiguity could result. This is merely a spelling convention; the u's here are still pronounced ü.
1 wei: ui is actually an abbreviation of uei. This is why Hanyu Pinyin uses, for example, shui, not shuei, and dui, not duei.
2 wen: un is actually an abbreviation of uen.
3 you: iu is acutally an abbreviation of iou. Thus, since i is written y at the beginning of a syllable, the spelling becomes you instead of yu (which would be not only misleading but wrong).
er has been omitted from this table.