HOW TO ESTIMATE ANYTHINGLearning Night - 01/21/15

WHAT I’M TALKING ABOUT TODAY• What is a Fermi Estimation?

• An example to get us going…

• Some tips and tricks

• Try it yourself!

• Skeptical?

EVER WONDER HOW MANY OR HOW OFTEN SOMETHING HAPPENS?

HOW MANY PIANO TUNERS ARE IN SAN FRANCISCO?

PIANO TUNERS IN SF• 1M people in SF

• 2 people per household

• 1/20 households have a piano

• each piano tuned once a year

• 2 hours to tune a piano

• tuners work full time for 40 hours a week

THE MATH

• 1M people / 2 people per household = 500K households

• 500K * 1 / 20 pianos/household = 25 000 pianos = 25 000 piano tunings per year

• 1 hour to tune a piano = 100 000 piano tuning hours

• 100 000 hours / 2 000 hours per piano tuner = ~50 piano tuners!

USEFUL FOR…

• Interviews!

• Satisfying personal curiosity

• Trying to figure out whether or not Maroon 5 really crashed all those weddings…

TACTICS

• Top down vs. Bottoms up

• Give a range!

• Easy numbers = Good numbers

• Key is make assumptions based on what you know

HOW MANY PEOPLE ARE NAMED JONATHAN IN THE WORLD?

LOL. WHAT A DOUCHE.

• Jonathan is a Male name

• 50% of population is Male

• Only Westernized civilizations will name kids Jonathan (2B people)

• 1/16 Males named some variation of Jonathan (Jon, John, Johnathan etc)

• 3B * 50% * 1/16 = 62.5M people named Jonathan

SKEPTICAL?

• Fermi is for…

• quick estimates

• magnitude

• starting points

"FERMI ESTIMATES WORK BECAUSE THE ESTIMATIONS OF THE INDIVIDUAL TERMS ARE OFTEN CLOSE TO

CORRECT, AND OVERESTIMATES AND UNDERESTIMATES HELP CANCEL EACH OTHER OUT. "