Number, size and scale: estimationsSpec 1.4
In short
An estimation is an approximate answer, usually found by rounding numbers to one significant figure. In biology, estimations are used to check that a calculated answer is sensible, to find a value when an exact count is impossible or too slow, and to compare sizes quickly, such as roughly how many times bigger one cell is than another.
Biology deals with very big and very small numbers, from the number of cells in a body to the size of a ribosome. You need to understand number, size and scale so you can compare sizes sensibly.
An estimation is an approximate answer, usually found by rounding numbers to one significant figure. Estimations should be used:
- to check that the answer to a calculation is sensible, for example that a cell is not 5 metres long
- when an exact value is not needed, or is impossible or too slow to find, for example estimating the number of cells in a sample by counting a few areas and scaling up
- to make quick comparisons between sizes, for example roughly how many times bigger one cell is than another
To check a calculation, round first: 59 mm ÷ 410 is roughly 60 ÷ 400 = 0.15 mm. If your answer is nowhere near that, look for a slip with units.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026