Tables

The constants, in one place

Every value below is computed from the first table. The primers quote the same constants, so the tables and the text cannot disagree. Monoisotopic masses are exact to five decimals; average masses depend on the atomic weights chosen and can differ from other sources in the third decimal place.

Atomic masses

Element	Symbol	Monoisotopic (Da)	Standard atomic weight
Carbon	C	12.00000000	12.011
Hydrogen	H	1.00782503	1.008
Nitrogen	N	14.00307401	14.007
Oxygen	O	15.99491462	15.999
Sulfur	S	31.97207117	32.060

Monoisotopic: exact mass of the most abundant isotope (12C, 1H, 14N, 16O, 32S). Standard atomic weight: IUPAC abridged value, 2021.

Source: IUPAC Commission on Isotopic Abundances and Atomic Weights, standard atomic weights. Proton mass, for [M+H]⁺: 1.00727647 Da.

SI prefixes

Prefix	Symbol	Factor
kilo	k	×1,000
(none)	–	×1
milli	m	×10^-3
micro	µ	×10^-6
nano	n	×10^-9
pico	p	×10^-12

Each step is a factor of a thousand. See the primer on changing units.

Amino acid residues

A residue is the amino acid minus one water. The mass of a linear chain is the sum of its residues plus one water, as explained in The arithmetic of chains.

Residue	Codes	Residue formula	Monoisotopic (Da)	Average (Da)	Free amino acid, mono (Da)
Glycine	Gly · G	C₂H₃NO	57.02146	57.052	75.03203
Alanine	Ala · A	C₃H₅NO	71.03711	71.079	89.04768
Serine	Ser · S	C₃H₅NO₂	87.03203	87.078	105.04259
Proline	Pro · P	C₅H₇NO	97.05276	97.117	115.06333
Valine	Val · V	C₅H₉NO	99.06841	99.133	117.07898
Threonine	Thr · T	C₄H₇NO₂	101.04768	101.105	119.05824
Cysteine	Cys · C	C₃H₅NOS	103.00918	103.139	121.01975
Leucine	Leu · L	C₆H₁₁NO	113.08406	113.160	131.09463
Isoleucine	Ile · I	C₆H₁₁NO	113.08406	113.160	131.09463
Asparagine	Asn · N	C₄H₆N₂O₂	114.04293	114.104	132.05349
Aspartic acid	Asp · D	C₄H₅NO₃	115.02694	115.088	133.03751
Glutamine	Gln · Q	C₅H₈N₂O₂	128.05858	128.131	146.06914
Lysine	Lys · K	C₆H₁₂N₂O	128.09496	128.175	146.10553
Glutamic acid	Glu · E	C₅H₇NO₃	129.04259	129.115	147.05316
Methionine	Met · M	C₅H₉NOS	131.04049	131.193	149.05105
Histidine	His · H	C₆H₇N₃O	137.05891	137.142	155.06948
Phenylalanine	Phe · F	C₉H₉NO	147.06841	147.177	165.07898
Arginine	Arg · R	C₆H₁₂N₄O	156.10111	156.189	174.11168
Tyrosine	Tyr · Y	C₉H₉NO₂	163.06333	163.176	181.07389
Tryptophan	Trp · W	C₁₁H₁₀N₂O	186.07931	186.214	204.08988

Leucine and isoleucine are constitutional isomers and share every value in this table.

Small molecules

Compound	Formula	Monoisotopic (Da)	Average (Da)
Water	H₂O	18.01056	18.015
Glycine	C₂H₅NO₂	75.03203	75.067
Alanine	C₃H₇NO₂	89.04768	89.094
Leucine / Isoleucine	C₆H₁₃NO₂	131.09463	131.175
Glucose (anhydrous)	C₆H₁₂O₆	180.06339	180.156
Glucose monohydrate	C₆H₁₄O₇	198.07395	198.171
Caffeine	C₈H₁₀N₄O₂	194.08038	194.194

The monohydrate row is the anhydrous row plus one water: the molar mass to use when that is what is in the bottle.