How long should a Muslim man's beard be?

What the Prophet ﷺ taught

The Prophet ﷺ said: "Do the opposite of the polytheists: let the beard grow and trim the mustache" (Sahih al-Bukhari 5892). A similar wording is in Sahih Muslim 259. The Prophet ﷺ himself had a full, thick beard, and his example is the model Muslims try to follow.

Notice that the hadith tells you to let the beard grow; it doesn't give a number of centimetres. That's why scholars discuss length rather than set an exact rule.

The fist-length view

In the same narration, the narrator adds that Ibn Umar, when he did Hajj or Umrah, used to hold his beard in his fist and cut off whatever went beyond it (Sahih al-Bukhari 5892). Based on this, scholars hold different views:

• Hanafi and many Hanbali scholars: a fist's length is the standard; trimming the extra is fine, and shortening it below a fist is disliked or not allowed.
• Maliki scholars: trimming a very long beard so it looks tidy is good, without a fixed measure.
• Shafi'i scholars: it's better to leave it, though light trimming isn't sinful.
• Some scholars say it should never be cut at all, taking the hadith literally.

Shaving the beard completely is considered forbidden by most scholars of the four schools, while a minority (including some Shafi'i scholars) view it as strongly disliked rather than haram.

Neat, not neglected

A sunnah beard isn't meant to look messy. You can comb it, oil it, wash it in wudu and tidy stray hairs on the neck and cheeks. Trimming the mustache so it doesn't cover the lip is part of the same instruction. See What is fitrah hygiene in Islam?

If you're just starting

Many converts grow their beard slowly while their family and workplace get used to the new look. That's a normal process, and Allah sees the effort. See Do I have to grow a beard right away? For hair on the head, the rules are more relaxed; see Can Muslim men have long hair?