The ranat thum lek (Thai: ระนาดทุ้มเหล็ก, pronounced [ranâːt tʰúm lèk]) is a metallophone used in the classical music of Thailand.

It is the larger of the two sizes of Thai metallophones; the smaller one is called ranat ek lek.

The ranat thum lek consists of flat metal slabs placed over a rectangular wooden resonator.

The origin of this instrument is attributed to the brother of King Rama IV (1854–1868) the same time as the creation of roneat ek lek.

[1] The ranat thum lek is very similar to the Khmer roneat thong.