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Notes from the field ·

Teaching Estimation and Measurement in Science: Why Guess Before You Measure?

By Ahmed, founder

Measuring is the heart of experimental science, and estimating before measuring makes it more meaningful. An estimate gives students a sense of what’s reasonable, so they notice when a number looks wrong.

Why estimate first

  • Number sense. Students learn how big a centimetre, a gram or a second is.
  • Error catching. If you guessed 30 cm and measured 3 m, you probably misread the ruler.
  • Engagement. A guess creates a stake.

Benchmarks to teach

Length: a fingernail width is about 1 cm. A hand span is about 15 to 20 cm in a child. A large step is about 50 cm. A door is about 2 m tall.

Mass: a paper clip is about 1 g. A pencil is about 5 to 10 g. A litre of water is 1 kg.

Volume: a teaspoon is about 5 mL. A cup is about 250 mL.

Time: a heartbeat is about a second. A minute feels longer than you think.

Temperature: water freezes at 0 °C and boils at 100 °C (at sea level). Room temperature is about 20 °C. Body temperature is about 37 °C.

Activities

  1. Estimate, then check. Guess the length of five objects, measure and record the difference.
  2. Heft and rank. Rank bags by mass, then check on a balance. See Which weighs more, a kilogram of feathers or a kilogram of rocks?
  3. Time guess. Close your eyes and raise a hand after a minute. See How long is a minute, really?
  4. Whose foot? Measure with body units, then with standard units. See Whose foot is the right ruler?

Measuring well

  • Start at zero, and note where the ruler’s zero actually is.
  • Read at eye level to avoid angle errors.
  • Include units. “12” means nothing. “12 cm” does.
  • Round sensibly. Use the smallest mark on the tool.
  • Repeat and average to reduce error.

Accuracy and precision

A measurement can be close to the true value (accurate) and consistent when repeated (precise). Older students can discuss which matters for their experiment.

Metric and imperial

Use metric in science, and give imperial in brackets where helpful: “20 cm (8 in).” Help students move between them with benchmarks.

The whole Measure It unit is built on these ideas, ending with a paper airplane design test. Sign up for three lessons free.