Worked estimates
Each one builds an estimate from guesses with honest ranges, then checks it against a published figure. Open any of them, or start your own in the notebook or the editor.
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How many piano tuners work in Chicago?
Fermi's own question, worked from both ends (how many pianos need tuning, how many one tuner can handle) and then asking
sensitivity()which guess to research next. -
How much electricity does an American home use?
Nobody knows their fridge's wattage, but you can work it out from foam insulation and a heat pump. Building up a home's use from physics, one appliance at a time.
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How much gasoline does the US burn?
Two independent estimates of the same number, one from the cars on the road and one from the pumps at gas stations, reported in the barrels the EIA uses.
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How many GPU-hours did it take to train Llama 2?
FLOP and FLOP/s are units like any other, so a training budget falls out of the model size and the hardware spec. Then a function reuses the same reasoning to check a second, much larger model.
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How much electricity do the world's data centers use?
Nobody publishes a count of the world's servers, but vendors report how many they ship. The installed base is shipments times lifetime, and each server's draw comes from its parts.
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How much does Earth's atmosphere weigh?
Air pressure is the weight of the air overhead, so pressure times area gives a force. The units won't let you call that force a mass, and a second pass with the scale height of the atmosphere gets within 1% of the measured value.
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How many cups of tea do Britons drink a day?
A mixture describes one person who might drink no tea, a little or a lot;
mean()turns that into a national total. Then the heat capacity of water says what all that kettle-boiling costs. -
How many airline flights take off each day?
How many flights a plane makes in a day comes from distance, cruising speed and how long it sits at the gate. Multiply by the fleet and the hours cancel, leaving flights per day.