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November 2026 - Choosing the Right Unit Study Guide

Choosing a sensible unit is its own skill: millilitres for a medication dose, litres for daily fluid intake, grams for a dressing, kilograms for a patient. The right unit is the one that produces a manageable number — neither 0.00004 nor 4,000,000.

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Updated November 2026

Mathematics guide Measurement and data · 16 scored questions 6 min read

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Try 4 short questions throughout this guide. Check each answer to learn from the explanation.

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Two questions decide it

  • What kind of quantity is it? Length, mass, volume, time, temperature or area. Getting this wrong means an answer that is not just badly scaled but nonsensical — grams cannot measure a distance.
  • What scale is it? Once the quantity is right, pick the unit that puts the figure between roughly 1 and 1,000.

The usual choices

MeasuringUnitWhy
A patient's weight kilograms A typical adult is 50–120 — a workable range
A tablet's active ingredient milligrams Grams would give figures like 0.005
A single medication dose millilitres Litres would give 0.005 L
Daily fluid intake litres Millilitres would give figures in the thousands
A wound centimetres or millimetres Metres would give 0.03 m
A corridor metres Centimetres would give figures in the hundreds
A journey kilometres or miles Metres would give tens of thousands
Body temperature degrees Celsius The scale medicine uses
A dressing or a swab grams Kilograms would give 0.004 kg

Precision follows the unit. A patient's weight recorded to the nearest kilogram is sensible; a neonatal weight is recorded in grams because a kilogram is too coarse to be safe. Where the answer changes a decision, the unit has to be fine enough to carry it.

Question 1 of 4

Which unit is most appropriate for recording an adult patient's body weight?

Answer Choices for Question 1

View the Answer and Explanation

Correct answer: B. Kilograms

Kilograms put an adult in the 50–120 range, which is readable and precise enough. Grams would give figures in the tens of thousands, milligrams in the millions, and millilitres measure volume rather than mass at all.

Choosing and checking

Worked example

Which unit should be used to record the amount of a drug in a single tablet, given a typical amount of 0.0005 of a gram?

  1. Identify the quantity: mass.
  2. Try grams: 0.0005 g — four leading zeros, easy to misread by a factor of ten.
  3. Try milligrams: 0.5 mg — readable.
  4. Try micrograms: 500 mcg — also readable, and the usual convention below 1 mg.

Micrograms, or milligrams if the figure stays at or above 1 mg. Grams is technically correct and practically unsafe, because a leading string of zeros is where decimal errors happen.

Question 2 of 4

A nurse needs to record the area of a pressure sore. Which unit is appropriate?

Answer Choices for Question 2

View the Answer and Explanation

Correct answer: B. Square centimetres

Area is two-dimensional, so it takes square units, and square centimetres are the right scale for a wound. Plain centimetres measure a single dimension, while millilitres and grams measure volume and mass.

Common mismatches the exam offers

  • A unit of the wrong quantity — millilitres for a weight, grams for a length.
  • A unit three orders of magnitude out — kilograms for a tablet, millimetres for a corridor.
  • A unit that is fine in principle but produces a figure nobody could read at a glance.
  • An area answered in linear units, or a volume answered in square units.

Terms to know

Unit
The standard quantity a measurement is expressed in.
Magnitude
The scale of a value, in powers of ten.
Precision
How finely a measurement is recorded.
Micrograms
One thousandth of a milligram, written mcg. Used where milligrams would be a decimal.
Square units
The units of area, such as cm². Length units cannot express area.

What the TEAS asks most

The same core ideas appear in different wording. If you can answer these without stopping to think, you have what this section requires.

Which unit is most appropriate for measuring X?

The one that matches the quantity and yields a figure roughly between 1 and 1,000.

Which of these measurements is unreasonable?

The one whose unit is the wrong quantity, or whose magnitude is impossible for the thing described.

Which unit would a nurse use to record this?

Clinical convention: kilograms for weight, millilitres for volume, milligrams or micrograms for drug quantities.

Question 3 of 4

A drug is present at 0.00025 grams per tablet. How is this best expressed?

Answer Choices for Question 3

View the Answer and Explanation

Correct answer: B. 0.25 mg, or 250 mcg

Shifting from grams to milligrams gives 0.25 mg, and to micrograms gives 250 mcg — both readable, with micrograms preferred below 1 mg. The original grams figure invites a decimal error, while 250 mg and 0.25 mcg are out by a factor of a thousand in each direction.

Key points

  • Match the quantity first — length, mass, volume, time, temperature, area.
  • Then match the scale: aim for a figure between about 1 and 1,000.
  • Millilitres for doses, litres for daily intake, kilograms for patients, milligrams for drug content.
  • Below 1 mg, use micrograms rather than a decimal fraction of a milligram.
  • Area takes square units; a length unit cannot express it.

Question 4 of 4

Which of these measurements is unreasonable?

Answer Choices for Question 4

View the Answer and Explanation

Correct answer: C. A single tablet weighing 5 kg

Five kilograms is roughly the weight of a small child, so it cannot describe a tablet — the unit is the right quantity but six orders of magnitude out. The other three are all ordinary clinical measurements at sensible scales.

TEAS · Identifying appropriate units of measurement

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