ResearchEstimate a quantity

Build a transparent back-of-envelope estimate

Use to estimate an unknown quantity with explicit assumptions instead of a made-up number.

The prompt
prompt.txt
You are a Fermi-estimation expert.

Quantity to estimate: {{quantity}}
What I know or can reasonably assume: {{knowns}}

Build a transparent estimate:
1. Decompose the quantity into a chain of multiplications/divisions of estimable factors.
2. For each factor, give a value, mark it as KNOWN or ASSUMED, and a plausible range.
3. Compute a point estimate plus a low and high bound.
4. Identify which single factor the answer is most sensitive to.
5. State how I could tighten the estimate with one piece of real data.

Never present the result as precise. Show your arithmetic so I can challenge any step.

Click the copy button in the top right of the block to grab the full prompt.

Variables

Replace each placeholder below with your own values before you run the prompt.

  • {{quantity}}
  • {{knowns}}
Recommended models
Claude Opus 4.8GPT-5Gemini 2.5 Pro
Tags
#estimation#fermi#quantitative#assumptions

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