Units of measure
Use the metric system with decimal fractions and multipliers. Basic SI units (meter, kilogram, etc) may be used, but use liter for volume and degrees Celsius (°C) for temperature. Specialized units, such as S – Svedburg unit (for sedimentation coefficient) or E – Einstein (as a unit of light irradiance) should be used where appropriate.
To express multiple units, different styles are permitted so as to maximize clarity in each instance. To indicate division between two units, a solidus (“/”) should normally be used. Examples include µg/ml and m/s2. Where multiple units are used, it will sometimes be appropriate to use “bullets” to indicate multiplication in units of measure. For example, light intensity could be expressed µE•s-1•m-2. In other cases, using the common derived SI units will be clearer. For example, use joule (J) instead of kg•m2•s-2.
Write out units that are not preceded by a number (e.g., the number of cysts per cubic centimeter of soil increased with time). There are no plural forms for unit abbreviations, e.g., ml (not mls).
Spell out numbers at beginning of sentence (e.g., four milliliters) and if a number is not specified, use “several” milliliters (i.e., spelled out, not abbreviated). Twenty-five milliliters was (not “were”) added to the solution (because all 25 ml are dumped in at once - considered as an entire unit of measurement).
Include a space between the numeral and the unit of measurement (e.g., 1.2 g, 3 ml, 1.2 g/liter). There are several exceptions (e.g., g , °C - degrees Celsius, 16S).
Common unit abbreviations:| bp | base pair | cm | centimeter |
| d | day | g | gravity (note italic) |
| ha | hectare | g | gram |
| hr | hour | kb | kilobase |
| kg | kilogram | km | kilometer |
| liter | always spell out in full | ml | milliliter |
| m | meter | min | minute |
| mon | month | sec | second |
| wk | week | yr | year |
log x, log (x + 1), log 10 x (note spacing). In text....“were transformed by x1 = log10 (x + 1) before analysis,” “....were transformed by arcsin ( √ x) before analysis” (not...“were log- transformed (log10 [x + 1]) or arcsin transformed”).
[ 3H]leucine (no hyphen or space), sodium [1-14C]acetate.
1.3 x 10 -4 (note spacing)
Decimal Fractions and Multiples:| FRACTION | PREFIX | SYMBOL |
| 10-1 | deci | d |
| 10-2 | centi | c |
| 10-3 | milli | m |
| 10-6 | micro | ?? |
| 10-9 | nano | n |
| 10-12 | pico | p |
| 10-15 | femto | f |
| 10-18 | atto | a |
| MULTIPLE | PREFIX | SYMBOL |
| 10 | deca | da |
| 102 | hecto | h |
| 103 | kilo | k |
| 106 | mega | M |
| 109 | giga | G |
| 1012 | tera | T |
Basic SI units:
| PHYSICAL QUANTITY | UNIT | SYMBOL |
| Length | metre | m |
| Mass | kilogramme | kg |
| Time | second | s |
| Electric current | ampere | A |
| Thermodynamic temperature | kelvin | K |
| Amount of substance | mole | mol |
| Luminous intensity | candela | cd |
Common derived units:
| PHYSICAL QUANTITY | UNIT | SYMBOL |
| Frequency | hertz | Hz |
| Energy | joule | J |
| Force | newton | N |
| Pressure | pascal | Pa |
| Power | watt | W |
| Electric charge | coulcomb | C |
| Electric potential difference | volt | V |
| Electric resistance | ohm | O |
| Electric conductance | siemens | S |
| Electric capacitance | farad | F |
| Magnetic flux | weber | Wb |
| Inductance | henry | H |
| Magnetic flux density (induction) | telsa | T |