fmole

Fmole, or femtomole, is a unit of amount of substance equal to 10^-15 moles. It is a submultiple of the mole, used to express extremely small quantities in chemistry and biology. The symbol is fmol. As with other SI-derived prefixes, femto denotes a factor of 10^-15, so a femtomole is one quadrillionth of a mole.

One fmol corresponds to about 6.02×10^8 molecules (using Avogadro's constant 6.02214076×10^23 mol^-1). The mass of one fmol of a substance with molar mass M g/mol is M × 10^-15 grams. For example, one fmol of water (M ≈ 18.015 g/mol) has a mass of about 1.8×10^-14 g.

Fmoles are commonly used when quantifying very small amounts of material, such as nucleic acids, peptides, enzymes, or other biomolecules, in molecular biology and analytical chemistry. In practice, measurements are often reported in fmol or converted to pmol or amol depending on the scale of the assay. While not a separate SI unit, fmole serves as a practical abbreviation for reporting minute quantities that would be unwieldy in moles alone.