Short answer: "thank you" in French is Merci, or Merci beaucoup depending on the situation.
Merci, the core translation
The default way to say "thank you" in French is Merci. Pronounced roughly mehr-SEE.
When French speakers actually use it
"Merci beaucoup" adds emphasis. "Merci bien" is warmer.
Alternative: Merci beaucoup
Merci beaucoup is the other option French speakers reach for in this situation. It's not a synonym so much as a register shift, use the one that matches who you're talking to.
Practice this in a real French conversation
Reading a phrase and saying it out loud are two different skills. Skala's AI conversations let you drop "Merci" into a real French exchange in your first 3-minute lesson, so it sticks the first time.
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FAQ
What's the most polite way to say "thank you" in French?
Both Merci and Merci beaucoup are polite. Pick based on who you're talking to: register, not translation, is what natives are tuning into.
How do I pronounce Merci?
Roughly mehr-SEE. Recording yourself once and comparing to a native audio inside Skala closes the gap faster than reading pronunciation guides.