A floral formula is a notation for representing the structure of particular types of flowers. Such notations use numbers, letters and various symbols to convey significant information in a compact form. They may represent the floral form of a particular species, or may be generalized to characterize higher taxa, usually giving ranges of numbers of organs. Floral formulae are one of the two ways of describing flower structure developed during the 19th century, the other being floral diagrams. The format of floral formulae differs according to the tastes of particular authors and periods, yet they tend to convey the same information.

A floral formula is often used along with a floral diagram.

Floral formulae were developed at the beginning of the 19th century. The first authors using them were Cassel (1820), who first devised lists of integers to denote numbers of parts in named whorls, and Martius (1828). Grisebach (1854) used 4-integer series to represent the 4 whorls of floral parts in his textbook to describe characteristics of floral families, stating numbers of different organs separated by commas and highlighting fusion. Sachs (1873) used them together with floral diagrams; he noted their advantage of being composed of "ordinary typeface".

Although Eichler widely used floral diagrams in his Blüthendiagramme, he used floral formulae sparingly, mainly for families with simple flowers. Sattler's Organogenesis of Flowers (1973) takes advantage of floral formulae and diagrams to describe the ontogeny of 50 plant species. Newer books containing formulae include Plant Systematics by Judd et al. (2002) and Simpson (2010). Prenner et al. devised an extension of the existing model to broaden the descriptive capability of the formula and argued that formulae should be included in formal taxonomic descriptions. Ronse De Craene (2010) partially utilized their way of writing the formulae in his book Floral Diagrams.

The formula expresses counts of different floral organs; these are usually preceded by letters or abbreviations according to the organ type. They are ordered corresponding to the arrangement of the parts of the flower from the outside to the inside:

The labels with darker backgrounds are less common. "V" used by Prenner et al. for the number of ovules per gynoecium is followed by lowercase letter describing the type of placentation. For epicalyx/calyculus, the letter "k" is used.

The numbers are inserted after the labels, they may be formatted as sub- or superscript. If an organ is absent, its number is written as "0" or it is omitted, if there are "many" (usually more than 10–12) instances, it can be written as "∞". Whorls of the same organ are separated by "+". Organ counts within a whorl can be separated by ":", for example when part of the whorl is morphologically different. A range can be given if the number is variable, e.g. when the formula summarizes a taxon.

Groups of organs can be described by writing the number of instances in the group as superscript.