All needle gauges have millimeter and half sizes, unless otherwise noted.
Chiaogoo is a good choice if you are looking for a ulta-lightweight option. Manufactured in the USA this 5″ (12 cm) needle gauges is made of durable plastic.
Knitter's Pride Needle View Sizer has a magnifier to help with see your stitches when trying to determine gauge. It measures 6" by 2 1/4".
Knitter's Pride Round View Sizer is about 2 1/2" in diameter. Made of durable plastic.
Susan Bates' Knit Chek does not have options for sizing US 1 1/2 (2.5mm) and US 2 1/2 (3mm) needle sizes, and does not note mm sizing. Made of metal, this needle gauge is indestructible and has been around for so long that it is almost iconic. It measures 5" by 3".