Fermi Estimation Scratch Work Guide
Fermi estimation scratch work guide for target units, factor trees, assumptions, unit checks, final ranges, and review.
Candidates who lose track of assumptions and units during estimates.
Start with the target
Write the exact target quantity and unit at the top. This anchors the whole estimate and keeps the final answer on task.
Draw a factor tree
Use a simple product or sum of drivers. Each factor should have a unit and a rough assumption value that can be challenged or revised.
Concrete layout
For revenue, write users x transactions per user x price. Then add the time period and final unit before multiplying so the target stays clear.
Reserve a check line
End with a scale check, range, and dominant assumption. This makes the review visible instead of an afterthought after the arithmetic.
Common mistakes
Candidates often over-format the page and slow down. Use just enough structure to preserve units and assumptions while keeping momentum.
Practice the pattern
Use the LeetQuidity curriculum and calibration to turn this topic into a focused practice plan.