How heavy is a frag grenade?

It depends on what kind of grenade it is.

The M26 and M26A1 grenades are 21 oz (595 g).

The M61 grenade is 16 ounces (453 g).

The M67 grenade is 14 ounces (397 g).

The MK2 grenade is 21 ounces (595 g).

The No. 5 Mark I Mills grenade is 22.5 ounces (638 g).