Basic, lesson 1 of 3
Anchor numbers and clean rounding
A handful of round numbers carries most sizing questions. Memorize them, round on purpose, and say that you are rounding.
7 min, 3 checks
1The anchors worth knowing
| Anchor | Round figure | Use it for |
|---|---|---|
| US population | About 330 million | Consumer products, per person checks |
| US households | About 130 million, about 2.5 people each | Appliances, utilities, subscriptions |
| People per year of age | About 4 million (330M spread over about 80 years) | Age bands: students, new drivers, retirees |
| Working year | About 50 weeks, 250 working days, 2,000 hours | Labor costs, B2B usage, utilization |
| Hours in a year | 8,760 | Capacity of anything that runs around the clock |
The flat age curve is a simplification: there are fewer people over 80, and birth cohorts differ. For a sizing case it is close enough, and saying so out loud earns credit.
Check 1
Using about 4 million people per year of age, how many Americans are 18 to 22 years old (five ages), in millions?
Check 2
A machine runs 24 hours a day, 365 days a year, at 90% uptime. How many hours does it run a year? Round to the nearest whole hour.
2Rounding on purpose
Round each input to a number you can multiply in your head, and round in opposite directions when you can so the errors cancel. 330 million times 28% is hard; 330 times 30% is 99, call it 100 million, and note you rounded up twice.
Keep units on every line: people, households, units per year, dollars per unit. Most sizing errors are a lost zero or a monthly figure multiplied as if it were annual.
Check 3
Which anchor should a dishwasher sales estimate start from?
Terms in this lesson: Utilization.
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