The problem is the gap, not the bag
Most flights from Europe and North America land in Bangkok in the morning. Most hotel rooms are ready in the afternoon. That gap is where the question comes from, and it has three sensible answers depending on where you will be during it.
If you are going to your hotel's neighbourhood anyway, store there. If you are spending the gap at the airport, store at the airport. If you are moving between cities that day, store at whichever end you will return to.
Storing at your accommodation
This is the default and it is usually free. Message the property before you arrive with your flight number, ask them to hold your bags from a stated hour, and get the confirmation in writing. Bangkok hotels handle this every day and the request is unremarkable.
Two practical notes. Take a photo of your bag as you hand it over, and take the tag or receipt seriously if one is issued. And be realistic about what you leave: reception storage is a room behind a desk, not a safe.
Storing at Suvarnabhumi
The airport publishes a left luggage service run by Bellugg with two counters in Terminal 1: on the second floor near the Tourist Police, and on the fourth floor behind check-in Row P. Published fees are 100 baht per 24 hours for a small bag, 150 for a medium and 200 for an oversized item, with additional part-day charges after that, and items unclaimed after 180 days become the facility's property.
You get a receipt, and you need identification to collect. Keep both together, and photograph the receipt in case the paper goes missing in a pocket during a long day.
| Where | Best for | Watch out for |
|---|---|---|
| Your hotel | Anyone with a booking in the city | Storage is a back room, not a safe |
| Suvarnabhumi Terminal 1 | Layovers and early departures | Fees run per 24 hours, not per hour |
| Left luggage shops in the city | Days that start and end elsewhere | Verify the shop is actually open at your return hour |
What to carry with you
Keep your passport, phone, charger, cards, cash and any medication on your person. Add a change of shirt if you have arrived overnight and plan to be out until check-in, because Bangkok in the afternoon will find every seam of a shirt you slept in.
Everything else can go into storage. A day with a small bag rather than a suitcase is the difference between using the trains and boats comfortably and hauling a case up a footbridge in the heat.
Before you head into the city
Note the closing hour of wherever you left your bags, and set an alarm for an hour before it. The commonest way this goes wrong is not theft; it is misjudging traffic on the way back and arriving at a shuttered counter with a flight to catch.