Fill up means to fill something completely, to the top, including filling a car's tank. People say it about a glass, a tank and a room that gradually fills with people: The café filled up by noon.
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fill up (with + thing); fill + it/sth + up; fill up the car/tank; fill up on + food
- I need to fill up the car before we drive to the coast.
- The lecture hall filled up quickly, so we had to sit on the stairs.
- Don't fill up on bread, the main course is huge.
What changed
First versionPlease fill up this form and bring it to reception.
RevisionPlease fill in this form and bring it to reception.
Up can seem to mean “completely”, so fill up a form feels logical. But fill up is about filling a container: a tank, a glass, a hall. The blanks on a form are filled in, and in American English more often filled out.
Top up means to add more to something that's already partly full: Can I top up your glass? It's also how you add credit to a phone or a travel card: I need to top up my phone. Fill up isn't used here.
Your turn
The petrol light came on, so we stopped at the next station to ___ the tank.
Show the answer
fill up — The fuel warning light came on, so the tank needs filling: fill up. You fill in a form or the gaps in a text, not a tank.
Describe a car journey. Say where you had to stop and why.
On our drive to Kazan, we stopped in a small town to fill up the car and buy some snacks.
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