Quick answer: Fast = moving at high speed (a fast car, run fast). Quick = taking little time, done promptly (a quick question, quick thinking). Fast describes the speed of movement or rate; quick describes the brevity of the time taken. In practice they often overlap, but the distinction matters when choosing the right adjective before a noun. For a fuller definition, see the Cambridge Dictionary entry for ‘quick’.
At a Glance: Quick vs Fast
Both quick and fast relate to speed, and native speakers use them interchangeably in many situations. However, there is a useful distinction: fast focuses on how rapidly something moves or operates, while quick focuses on how little time something takes. This explains why we say a fast car (high velocity) but a quick shower (not long in duration).
| Word | Part of Speech | Core Meaning | Examples |
|---|---|---|---|
| fast | adjective / adverb | moving at high speed; happening at a rapid rate | a fast car / She runs fast. / fast internet / a fast typist |
| quick | adjective / adverb | done in a short time; prompt; without unnecessary delay | a quick question / Be quick! / quick thinking / a quick look |
Using “Fast”
Fast is the word for describing high velocity, speed of movement, or a high rate of activity. When something moves at speed — a vehicle, a runner, a network connection, a machine — we reach for fast. It focuses on the rate at which something moves through space or the rate at which something happens over time.
Common collocations with fast:
- a fast car / train / runner — high physical speed
- fast internet — high data transfer rate
- fast food — originally meant cooked and served rapidly (now a cultural category)
- a fast learner — someone who acquires skills at a high rate
- speak fast — speaking at a high rate of words per minute
- a fast typist — types many words per minute
- fast asleep — a fixed phrase meaning deeply asleep (not related to speed)
Notice how all of these involve an inherent sense of rate or velocity, not just brevity of time.
Fast: Adjective and Adverb
One of the most important grammar points about fast is that it functions as both an adjective and an adverb with the same form. There is no word “fastly” — this is a very common mistake among learners.
She is a fast driver. (adjective before noun)
She drives very fast. (adverb after verb)
She drives very fastly. (not a word — do not use)
If you want an adverb ending in -ly to describe speed, use quickly: She moved quickly across the room. Both fast and quickly are correct adverbs; fastly does not exist.
Using “Quick”
Quick focuses on the short amount of time something takes rather than on its physical speed. When you describe an action as quick, you are saying it did not take long — it was prompt, brief, or done without delay. This is why quick pairs naturally with tasks and actions that can be completed in a short time.
Common collocations with quick:
- a quick question — one that won’t take long to answer
- a quick lunch — a brief lunch break
- a quick look / glance — a brief visual check
- a quick decision — made without lengthy deliberation
- a quick shower — a brief shower, not necessarily high-pressure
- quick thinking — the ability to think and react promptly
- quick to respond — responding without delay
Notice that none of these involve physical velocity — they are all about how little time something requires.
“Quickly” vs “Fast” as Adverbs
As adverbs, quickly and fast both describe how rapidly an action is performed. In many sentences, they are interchangeable:
She ran quickly to catch the bus.
She ran fast to catch the bus.
However, subtle differences remain. Fast emphasises pure speed (how rapidly she moved); quickly can also suggest that something was done in a short period without necessarily implying high speed: “He quickly made a decision” — the decision did not take long, but it does not suggest he was moving fast.
Quickly is also slightly more formal and versatile as an adverb. In academic and formal writing, quickly is preferred over fast in adverb position.
Side by Side: Quick vs Fast
These examples highlight when each word works best:
He drives a fast car. (the car has high velocity)
We took a quick trip to the shops. (the trip was brief in time)
She’s a fast reader. (reads many pages per hour)
She gave a quick reply to the email. (replied promptly, without delay)
The train is very fast. (high-speed train)
I just need a quick word with you. (a brief conversation)
Common Mistakes to Avoid
Mistake 1 — Using “fastly”
“Fastly” is not a word in standard English. Use fast as an adverb (she ran fast) or use quickly (she ran quickly). Never write or say “she ran fastly” or “he moved fastly.” This is one of the most common grammar errors among intermediate learners.
Mistake 2 — “a quick driver” when you mean speed
If you mean someone who drives at high speed, say “a fast driver.” A “quick driver” could imply someone who makes rapid decisions behind the wheel, not necessarily someone who goes at high speed. When physical velocity is the focus, choose fast over quick.
Mistake 3 — “I need a fast shower”
While a native speaker would understand this, the more natural and idiomatic phrase is “a quick shower” (short in time). We don’t typically talk about the velocity of a shower — we talk about how brief it is. Similarly: a quick coffee, a quick nap, a quick chat — all of these are about brevity, not speed.
Related Confusing Word Pairs
- Same vs Similar — identical vs alike in some ways
- Near vs Nearby — preposition vs adjective
- Other vs Another — definite vs indefinite reference
- Fewer vs Less — countable vs uncountable quantities
Quick Quiz: Quick or Fast?
Choose the best word for each sentence.
1. “She’s a ___ typist — she types 120 words per minute.”
2. “Can I ask you a ___ question? It won’t take long.”
3. “He drives very ___.”
4. “We had a ___ lunch — only 10 minutes.”
Frequently Asked Questions
What is the difference between quick and fast?
Fast describes a high rate of speed or movement — it tells you how fast something moves. Quick describes how little time something takes — it tells you that something was brief or prompt. A fast car travels at high speed; a quick trip takes little time. In many cases they overlap, but the distinction shows most clearly in noun phrases: we say a fast car but a quick look.
Is “fastly” a word?
No. “Fastly” does not exist in standard English. The adverb form of fast is simply fast itself: She ran fast. If you want an adverb ending in -ly, use quickly: She ran quickly. Both are correct. Never write or say fastly.
Can “quick” and “fast” be used interchangeably?
In many sentences, yes. “She’s a quick runner” and “she’s a fast runner” are both perfectly natural. However, when choosing an adjective before a noun, the distinction matters: a fast car (high speed) sounds natural; a quick car sounds odd. A quick shower (brief) sounds natural; a fast shower sounds slightly strange to most native speakers.
What is “fast food” — fast or quick?
“Fast food” is a fixed compound noun that uses fast, not quick. It originally described food that was cooked and served rapidly. Today it is a cultural and commercial category — you cannot substitute quick food for it. This is an example of a fixed collocation where the two words are not interchangeable even though they are similar in meaning.
How do I use “quickly” vs “fast” as adverbs?
Both quickly and fast are correct adverbs. Fast is more common in everyday speech; quickly is slightly more formal and versatile. In academic or formal writing, prefer quickly. In natural conversation, both are common. Remember: never use fastly, which is not a word.
What are common collocations with “fast”?
Common collocations: fast car, fast train, fast internet, fast food, fast asleep, fast learner, speak fast, drive fast, run fast, fast pace, fast-growing, fast-moving. Also note the fixed phrase fast asleep (deeply asleep), which has nothing to do with speed — it is a survival from an older meaning of fast meaning “firmly” or “securely.”
What are common collocations with “quick”?
Common collocations: quick question, quick lunch, quick look, quick shower, quick decision, quick reply, quick thinking, quick fix, quick chat, be quick, quick to react. Many of these describe brief actions or prompt reactions. The phrase quick fix is a common idiom meaning a fast but possibly superficial solution to a problem.
Is “quick” more informal than “fast”?
Not significantly. Both words are used across all registers. However, quick may feel slightly more informal or conversational in certain contexts, while fast can sound more technical or precise (as in fast-growing market or fast data processing). In everyday speech, both are equally common and appropriate.
What does “think on your feet” have to do with quick vs fast?
The idiom “think on your feet” means to think and respond quickly and effectively in an unexpected situation. It is closely related to the concept of quick thinking — the ability to produce solutions promptly. Note that we say quick thinking, not fast thinking. This is because the focus is on the promptness and brevity of the mental response, not its speed as a physical process.
How are quick and fast used in sport and business English?
In sport, fast typically describes physical speed: a fast bowler, fast reflexes, a fast serve. Quick describes mental or reactive speed: quick feet, quick reactions, quick thinking under pressure. In business English, fast describes growth rates (fast-growing company) or processes (fast delivery), while quick describes prompt responses or brief actions (a quick turnaround, a quick meeting).