300,000,000 meters per second.
3.1416 or 22/7

square roots of primes
2= 1.4
3= 1.73
5= 2.236

27 cubic feet in a cubic yard
squares up to 225


sin number
birthday
postal codes
home address
home phone
The same for a few other select individuals

plate numbers
2.2 pounds in a kilo
C(9/5)+32 convert Celsius to Fahrenheit

More conversions. Some pretty rough and ready.
1 kilometer is 6 /10 of a mile.
100kph is 60 mph
3 meters is 10 feet
300mm is a foot
100mm is 4 inches
20 mm is 3/4 inches
25.4mm in an inch
5 US quarts in a real gallon.
4 liters in a US gallon.
30 miles per hour is 44 feet per second

365.25 days in a year. 12 months 52 weeks seven days 24 hours
360 degrees in a circle, grad. a gradient of 100 is 45 degrees
the diagonal of a 12 inch square is 16.97 but 17 is close enough.

1066 Norman Invasion.
1776 American Revolution
1789 French Revolution
1867 Dominion of Canada created.

There are a lot more numbers but to try and drag them up just seems like a lot of work.

The thing to me is that we all carry a lot of numbers we don't even realize are there and that we use without even thinking about them.