Thailand's national picture (see the Thailand guide) is that tipping is voluntary almost everywhere. Bangkok adds one more layer: the gap between everyday local prices and the high-end, tourist-facing venues the city is famous for — rooftop bars, five-star hotels, upscale restaurants — is unusually wide, and expectations shift accordingly.
At street food stalls and local restaurants, tipping is not expected at all — rounding up to the nearest 10-20 baht is a nice gesture, nothing more. At hotel restaurants, rooftop bars and tourist-oriented venues, check the bill for a service charge; if there isn't one, 5-10% is reasonable given the higher prices. Grab and metered taxis don't expect a tip, though rounding up is common if a driver has helped with luggage or handled bad traffic well.
Rooftop bars in particular are priced for tourists rather than locals, and card machines there sometimes prompt for a tip in a way that feels closer to Western norms — you're not obligated to follow the prompt, but it's not unusual for others to add 5-10% at that price point. Always confirm a taxi is using the meter before the ride starts; that matters more to your total cost than any tip decision at the end.
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