### International Units of Measurement

Jeff Lawrence (Z30)

1. Standard units of measurement in biology are given below. This table deviates from MKS standards in that the kilogram (mass) and Kelvin (temperature) are not standard in biology.
```Measure		Unit	Abbr.	Translation
Number		mole	mol	6.022x1023
Mass		gram	g	454 gram È 1 pound
Length		meter	m	.0254 meter = 1 inch; 1 m È 39 inches
Volume		liter	l	3.9 liters È 1 gallon
Concentration	molar	M	1 mole per liter
Time		second	s
Temperature	Celsius	C	1° = 9/5 F; 0° = 32 F; 100° = 212 F
Radioactivity	Curie	Ci	3.7x1010 disintegrations per second
Resistance (R)	ohm	W
Current (I)	ampere	amp
Voltage (V)	volt	V	V = I*R
Power (P)	watt	W (V*A)	P = I*V; P = I2*R
```
2. Units can be expressed with prefixes denoting tenfold multiples of base unit. For example, 1000 meters is 1 kilo-meter; 1000 micrograms is 1 milligram.
```Multiple	Prefix	Abbr.
10-18		atto-	a
10-15		femto-	f
10-12		pico-	p
10-9		nano-	n
10-6		micro-	m
10-3		milli-	m
10-2		centi-	c
10-1		deci-	d
101		deca-	D
102		hecto-	H
103		kilo-	k
106		mega-	M
109		giga-	G
1012		tera	T
```
3. Molecular weight is expressed as grams per mol. If a substance (e.g., NaOH) has a molecular weight of, say, 40 grams per mol, a 1 M solution would contain 40 g per l, or 4 g per 100 mL, or 40 mg/ml.

4. A 1 % solution can be approximated as 1 g of solute per 100 mL or final solution, or 10 mg/ml.
Last Update: Thursday June 19 2014
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Eric Kofoid eckofoid at ucdavis.edu