# Conversions

Shorthand: idupree.com/=

Sound pressure levels: /2012/sound-meter

## Cycles

- 1 hour = 3600 s
- 1 day = 24 hour = 1440 minute = 86400 s
- 1 week = 168 hour = 10080 minute = 604800 s (0.6 Ms)
- 1 week (awake, 7-hour sleeps) = 119 hour
- 1 week (awake, 11-hour sleeps) = 91 hour
- 1 moon
^{1}= 29.53 day ≈ 708.7 hour ≈ 42524 minute ≈ 2551443 s (2.6 Ms) - 1 30-day month = 30 day = 720 hour = 43200 minute = 2592000 s (2.6 Ms)
- 1 mean Gregorian year = 365.2425 day = 8765.82 hour = 525949.2 minute = 31556952 s (32 Ms)
- 1 typical human life ≈ 2 Gs (≈ 63 years; 3 Gs ≈ 95 years)

The Earth rotates at the equator at about 0.46 km/s = 460 m/s = 1700 km/h = 1000 mph.^{2} Multiply by cos(latitude) to get surface movement speed anywhere.

For example, Cambridge, Massachusetts is about 42°N and about 5 miles (8 km) east/west. The sun is overhead-and-directly-south 17 seconds later at the west end of Cambridge than the east end. The Connecticut River is about 75 miles (120 km) further west and experiences midday just over 4 minutes later.

## Because some of my instruments aren't in metric

- 1 quart (US, liquid) = 0.946352946 L exactly. 1 L ≈ 1.057 quart. They are just over 5% different.
- 3 teaspoons = 1 Tablespoons = 1/16 cup
- 1 pound (mass) = 0.45359237 kg exactly. 1 kg ≈ 2.20 pounds.
- 1 mile = 1609.344 m exactly. 1 km ≈ 0.62 mi; 1 mi ≈ 1.61 km; approx ratio 5:8. The "U.S. survey mile" is 1.000002 times the regular mile for historical reasons.
- 1 inch = 2.54 cm exactly.

synodic = length of time between one full moon and the next, based on the orbits of the moon about the earth and the earth/moon system about the sun; accurate to the number of significant figures I give for each figure↩

to 2 significant figures; I use Earth's mean radius 6371 km = circumference 40030km because "The difference between a sphere and a reference ellipsoid for Earth is small, only about one part in 300." -https://en.wikipedia.org/wiki/Figure_of_the_Earth↩