Relative formula mass (Mr) & percentage composition
Enter a chemical formula (including brackets and hydrates). This tool always shows working.
Chemical formula
Rounding:
0 dp
1 dp
Calculate Mr
Calculate % composition
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What formats are accepted?
Element symbols
: Ca, Na, Cl, Fe, Cu … (capitalisation matters)
Numbers
after symbols or brackets: H2O, Ca(OH)2, Al2(SO4)3
Nested brackets
are supported
Hydrates
: use dot
.
or middle dot
·
or
⋅
(e.g.
CuSO4·5H2O
)
This tool does
not
handle charges or state symbols (e.g.
SO4^2-
,
(aq)
)
Common misconceptions (quick reminders)
Brackets change subscripts
: Ca(OH)2 means O2H2, not OH2.
Capital letters matter
: CO is carbon monoxide; Co is cobalt.
Hydrate dot means “plus water”
: CuSO4·5H2O includes 5 water molecules.
Don’t type zero for O
: H20 is usually a typo for H2O.
Results
Enter a formula and choose an option.