From Suvarnabhumi (BKK) to downtown Bangkok:
Metered taxis cost around 350–450 THB (₹850–1,100) including tolls and the airport surcharge (50 THB). Travel time is usually 30–60 mins, but can stretch during peak traffic.
You pay the fare on the meter + tolls (usually 2 toll booths, ~25–50 THB each). The 50 THB airport fee is added at the end. Make sure the driver uses the meter – they normally do at the official taxi queue on Level 1.
Tip: Avoid the guys approaching you inside the terminal; stick to the official queue.
Alternative: Airport Rail Link to Phaya Thai is just 45 THB, then switch to BTS/MRT if your hotel is near a station. Much faster in rush hour.
From Don Mueang (DMK):
Taxi fare is a bit less, around 300–400 THB depending on traffic.
Bottom line: Meter taxi from BKK to Sukhumvit/Silom is roughly 400–500 THB all in. If you hit heavy traffic, add 50–100 THB.