Valuing Your Labor With
Fermi Estimation
(Super-scientific guesses)
But Really
Interview Questions!
Also great for technology
Also great for technology
provide the basis for a discussion
Also great for technology
provide estimates for a project
provide the basis for a discussion
Also great for technology
provide estimates for a project
estimate the feasibility of an opportunity
provide the basis for a discussion
Also great for technology
provide estimates for a project
estimate the feasibility of an opportunity
determine if an answer that you have obtained makes sense
provide the basis for a discussion
Also great for careers
provide cost estimates for a project
estimate the return on investment of an opportunity
determine if an offer that you have obtained makes sense in relation to the company's budget and the project
provide the basis for a discussion about a raise
The Technique:
The Technique:
Identify the components of the answer
The Technique:
Divide the problem into small steps
Identify the components of the answer
The Technique:
Identify all the information you have
Divide the problem into small steps
Identify the components of the answer
The Technique:
Identify all the information you have
Determine what you have enough information for to factor into your problem
Divide the problem into small steps
Identify the components of the answer
The Technique:
Identify all the information you have
Determine what you have enough information for to factor into your problem
Divide the problem into small steps
Make an order-of-magnitude guess for what you don't have
Identify the components of the answer
The Technique:
Identify all the information you have
Determine what you have enough information for to factor into your problem
Divide the problem into small steps
Solve each step
Make an order-of-magnitude guess for what you don't have
Identify the components of the answer
The Technique:
Identify all the information you have
Determine what you have enough information for to factor into your problem
Divide the problem into small steps
Solve each step
Combine each step into an answer
Make an order-of-magnitude guess for what you don't have
Identify the components of the answer
The Technique:
Guessing
Rounding makes things easier to calculate- we only really care about orders of magnitude
The Technique:
Guessing
Rounding makes things easier to calculate- we only really care about orders of magnitude
Item Exact Value Suggested Value (for faster calculation)
1 day 24 hours 25 hours
1 mile 5280 feet 5000 feet
1 yard 0.9144 meter 1 meter
1 foot 30.48 cm 30 cm
1 pound 453.6 g 500 g
1 hour 3600 seconds 4000 seconds
Identify all the information you have
Identify all the information you have
How many kilometers are there in a light-year?
(2 mins: put your answers in chat)
Identify all the information you have
How many kilometers are there in a light-year?
How long is a light-year?
(2 mins: put your answers in chat)
Identify all the information you have
How many kilometers are there in a light-year?
How long is a light-year?
c = 186,000 miles / second
(2 mins: put your answers in chat)
Identify all the information you have
How many heartbeats are there in a year for the entire world's population?
Divide and Conquer
How many heartbeats are there in a year for the entire world's population?
Divide and Conquer
How many heartbeats are there in a year for the entire world's population?
What smaller problems is this composed of?
Divide and Conquer
How many heartbeats are there in a year for the entire world's population?
What smaller problems is this composed of?
How fast does one person's heart beat?
Divide and Conquer
How many heartbeats are there in a year for the entire world's population?
What smaller problems is this composed of?
How fast does one person's heart beat?
How many heartbeats per year?
Identify all the information you have
For the average person, how many times will their heart beat during their lifetime?
What do we know?
What do we have to guess?
(2 mins: put your answers in chat)
Divide and Conquer
How many heartbeats are there in a year for the entire world's population?
What smaller problems is this composed of?
How fast does one person's heart beat?
How many people are there?
How many heartbeats per year?
Divide and Conquer
How many heartbeats are there in a year for the entire world's population?
Earth's population * Heartbeats per year
Divide and Conquer
How many heartbeats are there in a year for the entire world's population?
Earth's population * Heartbeats per year
2,400,000,000 heartbeats per year in the US
Career Examples
How much cloud spend does reducing server lag by 100ms save?
Assume all XHR queries currently take about ~ 1 second to process.
Divide and Conquer
Smaller Problems:
How many requests per hour do we need to serve?
How many servers do we need?
How much do servers cost?
Divide and Conquer
Smaller Problems:
How many requests per hour do we need to serve?
How many servers do we need?
How much do servers cost?
What would we need to guess about in an interview?
What don't we need to guess about when we're on the job?
Career Examples
How much cloud spend on our API servers does fixing one bug that causes an extra page refresh for each visitor save?
Assume all XHR queries currently take about ~ 1 second to process.
Career Example Homework
You're the principal engineer on a new feature that allows users who offer a hosting experience to also offer other services, for which your company gets a fee of 10% of the cost of service.
What information do you need to figure out the profit your company derives from this feature?