- There are about 15 thousand possible three-letter combinations.
- The volume of a sphere is half the volume of the same size cube
- There are a million seconds in two weeks (1,209,600)
- There are 100,000 seconds in a day (actually 86,400)
- There are 1,000 hours in a month (720 or 744)
- There are 10,000 hours in a year (actually 8,760)
- There are 250 working days in a year.
- There are about 2000 working hours in a year.
- There are about 6 billion people in the world (or 5 billion, for the purpose of easier calculation)
- People live to be about 100 years old (for easy calculation)
- The Earth is about 24 or 25 thousand miles around
- The radius of the Earth is about 6000 km
- The surface area of the Earth is about 400 trillion square metres
- The mass of the Earth is about 6 x 10^24 kg
- The mass of the sun is about one million earths
- It costs about $1000 a month to rent a billboard.

- William Shakespeare, "The Merry Wives of Windsor"

- Some guidelines for 'quick check' calculations.
- Numbers in the real world.
- Grannus' circle.
- The front gate of Esmerel.

Page maintained by the Mathemagician.