Fill up

• Fill a container → top up · fill to the brim
• Refuel → gas up · tank up · put fuel in
• Become full → get full · reach capacity
• Fill with emotion → well up · swell
• Occupy time or space → take up · eat up
• Satisfy hunger → be filling · stuff you
• Reach capacity (bookings) → sell out · book out
• Storage runs out → max out · run out of space

Up here is a completive particle — the same up as in eat up, drink up, finish up, use up, clean up. It adds the idea of completion, to the very end. Nothing rises.

The practical difference:

• "Fill the glass." — put some in · "Fill up the glass." — to the brim
• "I filled the tank." — neutral · "I filled up the tank." — full, done
• "The restaurant filled." — unusual · "The restaurant filled up." — natural

Learners often drop the up because their first language marks completion with a prefix (на-повнити, за-правити), and the English particle feels optional. It isn't quite: in the intransitive senses especially, fill up is the normal form and bare fill sounds wrong.

• ❌ "The restaurant fills fast." → ✅ "The restaurant fills up fast."

Fill up is separable, which means a noun object can sit on either side — but a pronoun can't.

• ✅ "Fill up the tank."
• ✅ "Fill the tank up."
• ✅ "Fill it up." (the famous one — what you say at a petrol station)
• ❌ "Fill up it."
• ❌ "Fill up them."

This is a hard rule across all separable phrasal verbs, and fill it up is the easiest one to burn into memory because you'll hear it in every road-trip film ever made.

The words link: fill up → /ˈfɪlˈʌp/ with no gap, and fill it up becomes /ˈfɪlɪɾˈʌp/ — "FILL-it-up" as one word, with the American flapped t.

• "Fill up the kettle, I'll get the mugs."
• "Could you fill my glass up?"
• "She filled the bucket up and carried it out."
• "Fill it up to the line, not past it."

• "I need to fill up before we get on the motorway." (intransitive — no object needed, the tank is understood)
• "Fill it up, please." (what you say to an attendant)
• "We filled up just outside Chișinău."
• "It costs about €70 to fill up now."

British speakers fill up with petrol, Americans fill up with gas or gas up. Both use fill up, so this one is safe everywhere.

• "The place fills up around eight, so let's book."
• "The train filled up at the next stop."
• "My inbox fills up whenever I take a day off."
• "Traffic's building — the road's filling up."

This is the sense where the up is least optional. Bare fill here sounds incomplete to a native ear.

• "Her eyes filled up." — the fixed phrase; eyes fill up = tears form, and the tears themselves usually go unmentioned.
• "He filled up with pride watching her present."
• "I filled up a bit, honestly." (BrE, gentle: I nearly cried)

• "Meetings filled up my entire Tuesday."
• "The retro filled up the last hour of the day."
• "I've got the afternoon free — fill it up however you like."

• "Boxes filled up the whole hallway."
• "The sound filled up the room."
• "Their logo fills up half the slide." (mild criticism — too much space)

• "Don't fill up on bread, the main course is huge." — fill up on X = eat too much of X too early, a very common fixed pattern.
• "Two slices and I'm filled up."
• "Soup doesn't really fill me up."
• "Rice fills you up cheaply."

• "The course filled up in a day."
• "Slots are filling up fast — book early." (standard marketing line)
• "The class is full up." — full up is the adjective form, informal and BrE-leaning.

• "The disk filled up overnight and took the service down."
• "Logs filled up /var again."
• "The queue's filling up faster than we can drain it."
• "Memory fills up after about six hours — there's a leak somewhere."

This is the sense you'll use most often at work, and it's usually intransitive: the thing fills up by itself, and that's the problem.

• ❌ "Please fill up the form" → ✅ "Please fill in the form" (BrE) / "fill out the form" (AmE)
• ❌ "Fill up your details below" → ✅ "Fill in your details below"
• ❌ "I filled up the application" → ✅ "I filled out the application"

You fill up containers. You fill in or out documents. Заповнити covers both in Ukrainian and Russian; English does not.

• ❌ "Fill up by water" → ✅ "Fill it up with water"
• ❌ "Fill up of petrol" → ✅ "Fill up with petrol"
• ✅ "Fill up on bread" — the eat-too-much sense really does take on.

• ❌ "Fill up the glass completely to the full" → ✅ "Fill up the glass" — the up already says it.
• ❌ "Fill up full" → ✅ "Fill it up"

• ❌ "Fill up it" → ✅ "Fill it up"
• ❌ "I filled up my with fuel car" → ✅ "I filled my car up with fuel" / "I filled up my car with fuel"

• fill up — to capacity. "Fill up the tank."
• fill in — complete a document (BrE); also brief someone; also fill a hole. "Fill in the form." / "Fill me in." / "They filled in the pothole."
• fill out — complete a document (AmE); also gain weight or muscle. "Fill out the form." / "He's filled out since school."
• fill in for — substitute for a person. "I'm filling in for Anna this week."

• "Fill me in." = tell me what I missed. (after a holiday, after a meeting you skipped)
• "I'm filling in for him on Thursday." = covering his shift or role.

• fill → neutral, no endpoint implied.
• fill up → to capacity, completion.
• top up → add a bit more to something already partly full. Also phone credit in BrE: top up my phone.
• refill → fill again, after emptying. A noun too: a free refill.
• stock up → buy a lot in advance: stock up on coffee.
• load up → put a lot in or on: load up the van.
• run out → the opposite endpoint: we ran out of space.

Top up is partial. Fill up is total.

Top up adds. Fill up finishes. Refill repeats.

• Technical writing and monitoring alerts → prefer reaches capacity, is at 95% utilisation, exceeds the threshold. "The disk filled up" is what you say in the incident channel; "storage utilisation exceeded 95%" is what goes in the postmortem.
• Forms, always → fill in or fill out, never fill up.

• "I'll fill up on the way home."
• "Let's go early, it fills up by seven."
• "Fill me up a glass, would you?"
• "My calendar filled up before I could block any focus time."
• "Don't fill up on snacks, dinner's in an hour."

⛽ Tanks, glasses, disks and restaurants fill up. Forms get filled in (UK) or filled out (US). And if you only add a little, you top up.

1. fill in this form (BrE) — or fill out (AmE). Forms are never filled up.
2. Fill it up. Pronouns go in the middle of a separable phrasal verb, never after the particle.
3. on — the eat-too-much-too-early pattern takes on, not with.

1. What's the difference between “top up my coffee” and “fill up my coffee”? Top up = add a bit more to a partly full cup. Fill up = fill it to the top. Partial vs total.

2. Your colleague just got back from two weeks off. What do they say to you, using this verb family? "Fill me in." = tell me what I missed. Not fill me up — that would mean feed me.

3. Which sense is this, and is it transitive or intransitive: “The disk filled up overnight.” Sense 9, storage — and it's intransitive. The disk fills up on its own; that's exactly why it's a problem.

4. In fill up, what does up actually contribute? Name two other phrasal verbs that use up the same way. Up is a completive particle — to the limit, to completion, not upward. Same up as in eat up, drink up, use up, finish up, clean up.

5. Rewrite for a postmortem document: “The logs filled up the volume and everything died.” "Log growth exhausted available disk space on the volume, causing a service outage." Filled up is right for the incident channel, too casual for the write-up.

Roll out · Set up · Ship for the delivery vocabulary that pairs with capacity problems.