試着できますか

Catch a staff member's eye while holding the item. Point at the item and say the phrase clearly. You can add これ (kore) at the beginning. That means "Can I try *this* on?" It is simple, effective, and very polite. The staff will usually lead you to a room.

Use it at department stores, boutiques, or even thrift shops. It works for shirts, jackets, pants, and even hats. Use it whenever you are unsure about Japanese sizing. Japanese sizes often run smaller than Western sizes. It saves you from buying something that doesn't fit!

Don't use it for food samples at the supermarket. That requires a different word called shishoku. Avoid asking for sealed items like socks or underwear. Most shops won't allow those to be tried on. Don't say it to a friend's closet uninvited. That might feel a bit intrusive and strange!

Japanese retail service is famous for being incredibly attentive. Staff will often carry your items to the fitting room. They might count your items out loud for accuracy. You will often find a small face cover inside. This prevents makeup from staining the clothes. It is a unique and thoughtful touch.

For a slightly softer tone, try 試着してもいいですか (shichaku shite mo ii desu ka). If you just want the room, ask 試着室はどこですか. That means "Where is the fitting room?" Both will get you to the mirror eventually. Just remember to smile and be polite.