One half of the distance between the nuclei of two atom bonded together by a single bond is known as covalent bond radius. Covalent bond radius refers to half of the distance between two singly bonded atoms of the same element ( homonuclear X-X bond) and is denoted rcov. In other words, it is defined as half the covalent bond length when the two atoms bonded are homonuclear. rcov is typically measured by X-ray diffraction. When multiple allotropes exist for a given element, rcov is determined by averaging the bond distances found in each allotrope. Covalent radius is measured in picometers (pm) or ångströms (Å) and represents one measurement that is used in determining atomic radius.