Quantities, Fractions & Measurements

You stare at your homework. The sentence is sitting there: "Two-thirds of the class ___ planning the fair." Is or are? You type one, then delete it. Then the other. Then neither. Somewhere in the back of your mind a little voice says the verb should match the subject — you were taught that, and it's true — but what is the subject when the first word is a fraction and the next is of and the noun after that keeps changing its mind?

Here's the thing. That wobbly feeling is completely normal. Nobody's born knowing this — and I'll be honest, after twenty-two years of tidying up other people's writing for a living, it's still one I slow right down for. The good news is, the whole puzzle comes down to a single idea: is the quantity being treated as one lump, or as many separate things? Spot which is which, and the verb — almost always — falls into place. That's what we'll get straight here.

Before you read on, here's where we're heading. By the end of this article, you'll be able to: - Spot when a quantity is acting as one unit and when it's acting as many individuals. - Choose is / are (or was / were) with fractions and percentages that drag an of-phrase behind them. - Get measurements right — ten pounds is enough, not are. - Tell the number of and a number of apart without guessing. - Use a two-second test when a sentence feels like a trick.

Beginner (Foundation)

Let's start simple. Most of school grammar trains you to look at the main noun and make the verb match it — find the subject, match the verb, move on. Fair enough, and if you'd like that groundwork refreshed, head back to Pillar 1 for the basics of subject–verb agreement. But quantities are sneaky. Sometimes the "subject" is really an amount of something, and English often treats that amount as a single lump — even when the words sound plural.

Picture a cake. Someone says, "Two-thirds of the cake is gone." You're not imagining two separate thirds wandering off on their own. You're picturing one big missing chunk of cake — one unit. So we say is.

Now swap the thing being talked about: "Two-thirds of the biscuits are gone." Biscuits aren't one mass. They're separate, countable things — you can point at each one. The fraction still points at many individuals, so the verb stays are.

Same fraction. Different noun after of. Different verb. That little word of is doing the signal work — it points you straight at the thing that actually decides.

Measurements work the same way, only more so. When you say five miles, ten pounds, twenty minutes, you're nearly always talking about one distance, one sum of money, one length of time — so English treats them as a single total:

• Ten pounds is enough for the book.
• Five miles is too far to walk in this rain.
• Twenty minutes isn't long enough to finish the test.

You wouldn't usually say ten pounds are enough — as if the coins had each wandered off to do their own thing.

Common Mistake: Treating every plural-looking amount as plural. Ten pounds are enough? Not in this meaning. You're naming a sum, not counting coins one by one.

Pro-Tip: When you meet a fraction or percentage, lightly cover it with your finger and read the noun after the of. Singular thing like cake or water? Lean is. Plural things like biscuits or pupils? Lean are. The fraction was never the point.

Quick recap: - A quantity can act as one unit or as many things. - With an of-phrase, look at the noun after of to decide singular or plural. - Measurements of money, distance and time usually take a singular verb. - Ask yourself: "Am I talking about one total, or about separate items?"

Intermediate (Development)

Right — you've got the core idea. Now let's put it to work on the patterns that actually turn up in essays, science write-ups and exam papers.

Fractions and percentages with of

The standard pattern is easier than it looks:

• Fraction / percentage + of + singular or mass noun → singular verb. Two-thirds of the cake is left. Fifty per cent of the water has evaporated. Three-quarters of the homework is finished.
• Fraction / percentage + of + plural noun → plural verb. Two-thirds of the pupils are staying for practice. Fifty per cent of the answers were wrong. Three-quarters of the books have been returned.

Per cent behaves exactly like a fraction here — it's the noun after of that settles the verb, never the number itself. And keep it consistent: don't write "Half of the students is here, and the rest is at lunch." Once you've picked are for one, you want are for both — "Half of the students are here, and the rest are at lunch."

Measurements as lump sums

Money, distance, weight, volume, time — when you name them as a single figure, use a singular verb:

• Three kilos is more than we need for the recipe.
• Six months is a long time to wait for the trip.
• A hundred pounds was donated by the parents' group.

You'll sometimes see six months were, when the writer is genuinely thinking of the months as separate calendar squares ticking by. That's not "wrong" in every style guide — but in school writing the lump-sum = singular** habit is cleaner and it's what markers expect.

The number of versus a number of

This pair confuses almost everyone at least once. Let's be honest — the words look nearly identical. They aren't.

• The number of… is. You're talking about one figure — a count. The number of pupils in the quiz club is fifteen. The number of mistakes on the draft was small.
• A number of… are. This means roughly several, or quite a few — it's a soft way of saying many. A number of pupils are staying after school. A number of books were damaged in the rain.

Memory hook: the number points at one total → singular. A number of is just a posh some → plural.

Pro-Tip: Read the sentence out loud with several in place of a number of. If it still makes sense, you almost always want a plural verb. Several pupils are staying — yes. That check takes two seconds and saves a lot of red pen.

Common Mistake: Writing A number of students is missing because number looks singular. Ignore the word number for a moment — a number of behaves like some. Plural.

Quick recap: - Fraction / percentage of + singular / mass → singular verb; + plural → plural verb. - Lump-sum measurements (money, distance, time, weight) usually take singular. - The number of… is; a number of… are. - In doubt with a number of? Swap in several and listen.

Advanced (Mastery)

Once the patterns feel solid, the interesting bit is what to do when sense and form pull in different directions — and when you're writing for very different readers (a jokey blog, a formal report, a timed exam).

Notional agreement — quantity as an idea, not just a label

Sometimes writers choose the verb according to how they're picturing the thing, not only by the noun's outward shape. Ten pounds is almost always a lump sum (is), because you mean one amount of money. But ten lovely new pound coins invites you to see ten separate objects (are). Same currency — different mental picture, different verb.

Fractions tilt the same way when the focus shifts:

• Two-thirds of the team is signed up for the tournament. (the team as one block)
• Two-thirds of the team are bringing their own kit. (the members, one by one)

In British school and exam English, matching the noun after of is still the safer default. This flick between the "unit" reading and the "individuals" reading is one corner of a bigger idea called notional concord — for the full tour, see 5.7. And for indefinites that use the same of-phrase logic (each of, none of, all of), the sister article is 5.2.

Science, technical writing and register

In science and other technical subjects, writers nearly always treat measurements as a single unit, even where an everyday writer might waver:

• Ten grams of salt was added to the solution.
• Five litres of water is required.

The logic is that "ten grams" is one measured quantity — the fact that "ten" is more than one simply doesn't come into it. If you're writing a lab report, follow that convention and treat [number] + [unit] as singular.

Register matters in the other direction too. In relaxed chat you might hear "Fifty quid are nothing" from someone counting out notes — fine in speech. On a school essay, though, finish with is for the lump sum and move on. Greengrocers' signs and jokey mugs can do as they please. Homework can't.

Pro-Tip: When a sentence won't sit still, don't wrestle it — rewrite it. We collected ten pounds, which was enough is far cleaner than forcing an awkward verb onto a bare sum. Good writers dodge the choice all the time; it isn't cheating, it's editing.

Common Mistake: Mixing a very informal money word with a serious tone — "Five quid is a substantial amount" reads oddly not because of the verb (that's fine) but because quid has crashed a formal sentence. Match your words to your reader.

Quick recap: - Skilled writers notice whether they're picturing a unit or individuals, then match the verb to that picture. - School-safe default: match the noun after of; use singular for lump-sum measurements. - Science and technical writing treats measurements as singular units. - When a mid-way case won't settle, rephrase rather than force it. For the deeper "match the sense" idea, see 5.7; for nearby of-phrase patterns, see 5.2.

UK vs US Usage

The agreement rules in this article are shared across the Atlantic — nobody writes ten dollars are enough for careful prose. The one genuine, narrow difference is a spelling habit:

• UK English: usually per cent, two words — fifty per cent of the cake is**.
• US English: usually percent, one word — fifty percent of the cake is**.

The verb doesn't change; only the spelling does. And do keep the collective-noun question (the team is vs the team are) separate — that's a real UK/US split, but it belongs to Pillar 1, not here.

Key Takeaways

• Ask the unit-or-individuals question first: one lump → singular; many separate things → plural.
• With fractions and percentages, the noun after of decides the verb.
• Money, distance, weight and time as totals nearly always take a singular verb (ten pounds is**).
• The number of… is; a number of… are (≈ several).
• When the sense is muddy, rephrase — clean clarity beats a forced choice.
• UK/US: the agreement is aligned; per cent vs percent is the main cosmetic split. Collectives → Pillar 1.

Check Your Understanding

1. Choose the better verb: Two-thirds of the pizza ___ gone already. (is / are)
2. Choose the better verb: Two-thirds of the sandwiches ___ gone already. (is / are)
3. True or false? Ten pounds are enough for lunch is the usual school/exam choice for a sum of money.
4. Fill in: The number of entrants ___ thirty (is / are), and A number of entrants ___ late (is / are).
5. Why might a careful writer prefer Three kilograms of flour is needed over wrestling with a plural?

Internal Links

• Hub — Pillar 5 overview
• Pillar 1 — basic subject–verb agreement; collective-noun UK/US split (don't rebuild it here)
• Pillar 2 — quantifier / noun classification (back-link only; this piece doesn't re-teach fractions as a word class)
• 5.2 — the same of-phrase logic, applied to indefinites (all, some, none, each)
• 5.7 — notional concord (unit vs individuals at conceptual depth)
• Pillar 4 — verb forms / morphology (out of scope; link only if you need the is/are/was/were shapes themselves)

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