Fermi question · Everyday
About how many hairs are on a typical human scalp?
Make a fast, defensible estimate before you reveal the reference answer. Think in factors, not exact recall.
What is your estimate?
Your result will appear here after you submit a guess.
Reference answer
Reveal the reference answer
≈ 100 thousand hairs
Fermi estimates are judged by scale, so a reasonable approximation can still earn a strong score.
One way to estimate it
Estimate scalp area and how densely hair follicles are packed.
- Hair-bearing scalp area≈ 500 cm²
- Hair density≈ 200 hairs/cm²
- Estimate500 × 200 ≈ 100,000 hairs
Keep practicing
Try another question, or return to the daily challenge to build your personal sense of scale.
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