MEPX
Chapter 1 of 10All chapters
  1. 1Why estimate
  2. 2Anchors worth knowing
  3. 3Fermi estimates
  4. 4Rounding well
  5. 5Sanity checks
  6. 6Estimating percentages
  7. 7Estimating time
  8. 8Making big numbers real
  9. 9Where estimates go wrong
  10. 10Getting better

Chapter 1 of 10

Why estimate

Catching what precision hides.

The purpose

An estimate tells you whether an answer is plausible before you commit to it. A spreadsheet will happily report a town drinking 2,500 litres of water per person per day.

  • Being within a factor of ten is often enough to make a decision.
  • A wrong answer to six decimal places is still a wrong answer.

Where it pays

Sizing infrastructure, budgeting, checking a supplier quote, judging a headline statistic. Estimation is the everyday defence against confidently presented nonsense.