SI Unit Quiz Generator

The SI is unusual among quiz material in having no uncertainty at all: these names, symbols and relationships are fixed by international agreement rather than measured, so a question about them has exactly one right answer and always will. It is also the material students most often half-know — that a newton is force but not that it is kg·m·s⁻², that mega is a million but not that M and m are nine orders of magnitude apart.

Number of questions

How much to generate.

What to practise

Question type

Seed (optional)

Reproduces the identical set, for reprinting.

Your challenge will appear here.

What this generator does

Generates questions across three parts of the SI: the seven base units and the quantities they measure, the twenty-two named derived units and their definitions in base units, and the twenty-four decimal prefixes with their powers of ten. Prefix values are computed from the power rather than transcribed, so the number and the exponent shown beside it cannot disagree.

How to use this tool

Choose what to practise: base units, derived units, or decimal prefixes.
Choose multiple choice or reveal, and how many questions.
Press Generate.
Answer, then reveal to check.

Understanding the controls

What to practise: Base units are seven and worth knowing cold. Derived units are the twenty-two named ones, where the interesting question is what each measures. Prefixes are their own topic and the one where mistakes cost real money.
Question type: Multiple choice draws its wrong answers from the same set, so 'which quantity does the tesla measure' offers other real quantities. Reveal asks outright, which is much harder for derived units.
Number of questions: How many to generate. The base units are only seven, so a longer set on that topic will use each of them.

Worked examples

Base unit: The candela measures luminous intensity.
Derived unit: The newton is force — kg·m·s⁻² in base units.
Prefix: Nano is 10⁻⁹, or 0.000000001.
The costly one: M is mega and m is milli — a factor of a billion between them.

Common use cases

Physics and chemistry revision on units and prefixes
Engineering refreshers where prefix errors are expensive
Checking yourself on derived units before an exam
A quick round that has genuinely unambiguous answers

How this generator works

Every fact comes from the SI Brochure, which defines rather than measures — there is no sampling, no estimate and no source to disagree with. The base units are described by the quantity they measure rather than by any physical artefact, because since the 2019 redefinition none of them is an artefact; the kilogram has not been a lump of metal for years, and a page saying otherwise is simply out of date. Prefix values are generated from their power of ten at build time, so 'mega, 10⁶, 1000000' is arithmetic rather than three things typed separately.

Randomness and fairness

Question selection and option order use the browser's cryptographic random number generator. A seed switches to a reproducible generator so the same set can be repeated; that mode is deterministic, not cryptographic.

For how randomness is produced across the whole site, see how Generate Random works.

Assumptions this tool makes

Definitions follow the ninth edition of the SI Brochure, including the 2019 redefinition of the base units and the 2022 prefix additions.
Symbols are case-sensitive, which is a genuine part of the standard rather than a typographic preference.

Limitations and good to know

SI only. Imperial units, and non-SI units accepted for use with the SI such as the litre and the hour, are not covered.
It asks about definitions rather than conversions. Converting between units is a different exercise and a different tool.
The 2022 prefix additions — ronna, quetta, ronto and quecto — are included and are new enough that many textbooks predate them.
It generates and reveals; nothing is marked.

Common mistakes

Writing unit symbols in the wrong case: Case is part of the symbol. M is mega and m is milli; K is kelvin and k is kilo. A capital where a lowercase belongs can be a factor of a billion.
Thinking the kilogram is defined by a physical object: It was until 2019 and is not now. All seven base units are defined by fixed values of physical constants, which is why the definitions no longer mention an artefact.
Pluralising symbols: Ten metres is 10 m, never 10 ms — which would be ten milliseconds. Symbols never take an s.

Practical tips

Learn the seven base units first. Every derived unit is a combination of them, so they are the leverage.
For prefixes, learn the ladder in threes — kilo, mega, giga, tera — rather than as isolated facts. The pattern is what makes them stick.
Say what each derived unit measures rather than its formula. Knowing the pascal is pressure is more useful more often than knowing it is kg·m⁻¹·s⁻².

Troubleshooting

A prefix I have never seen appeared: Ronna, quetta, ronto and quecto were added in 2022 and are absent from most textbooks. They are current and correct.
The base-unit questions repeat: There are only seven base units, so any set longer than seven must reuse them. Switch to derived units or prefixes for a longer session.

Privacy and your data

Nothing is entered and nothing is stored. Questions are generated in your browser, never uploaded and never written into the page address. Analytics records only that the tool ran and which topic was chosen.

Frequently asked questions

How many SI base units are there?: Seven: the second, metre, kilogram, ampere, kelvin, mole and candela. Every other SI unit is derived from combinations of these, which is why they are worth knowing before anything else.
Why does case matter so much?: Because the case is part of the symbol, not a style choice. M means mega and m means milli, a difference of a factor of a billion; K is kelvin and k is kilo. Getting it wrong in engineering or medicine is a well-documented source of real errors.
Is this data likely to go out of date?: Less than almost anything else on this site. The SI is a definitional standard, so these are not measurements that get refined — they change only when the international body redefines something, which happened last in 2019 for the base units and 2022 for the newest prefixes.