Molecular formula
In short The number of atoms of each element in one molecule of the substance.
A molecular formula lists each element with the number of its atoms in one molecule. For BPC-157 it is C62H98N16O22: 62 carbon, 98 hydrogen, 16 nitrogen and 22 oxygen atoms. Peptides with sulphur-containing amino acids, such as methionine in Semax, add S; GHK-Cu includes a copper atom.
The formula does not describe structure. Different molecules can share a formula, so it is never used alone to identify a peptide. Together with the sequence and the CAS number, however, it is a useful consistency check: the molar mass calculated from the formula should match the mass found by mass spectrometry.
Formulas for modified peptides include the modification. An acetylated N-terminus or an amidated C-terminus changes the count of atoms, and a fatty-acid chain such as the one on tirzepatide adds many more. If a formula on a supplier's page does not fit the stated sequence, that is worth questioning.
On UKPeps product pages the formula is shown in the specification table, with subscripts, next to the molar mass.