However, in comparing Indian English to American English, in the US, we 'fill up' our gas tank (not petrol), or 'fill up our cup'. In the US, 'fill up' is typically used for pouring liquid to the brim of something. In the office, for instance, you may hear colleagues talking about "filling up the coffee pot."
So, in the US if you fill up a form, to Americanize this phrase, say, "fill out."
In India - "fill up" the form
In the US - "fill out" the form
Typically when some document needs to be completed by typing into it (filling out an online application) or writing by hand into it (filling out an immigration form on the plane, when landing in the US, for instance), Americans use the phrase, 'filling out' to describe this. If someone told an American 'I filled up the form,' I think the first image in their head would be pouring water on it. However, don't stress if you make this mistake. No one will get offended by it, it will just be a bit confusing for a moment.
To make it more complicated, the term "fill out" has a double meaning in American English, though! Don't worry once you hear the two definitaions, either will be easy to figure out by the context. And, the second definition would not be one we use in the office, anyhow, as it falls under 'avoidable' small talk topics!
Listen to Andrea of ESL Basics describe the two meanings of 'fill out' in the video below.
Author of this post, Jennifer Kumar is a cross-cultural business coach, helping non-Americans to understand the US business culture and language with more ease. If your company is hosting expats on international assignement in the US, contact us for training options.
Indian vs. American English at College
The Difference Between Phrasal Verbs, Idioms and Slang
Examples of Indian and US English Sentences