The Scherrer equation, derived by Paul Scherrer in 1918, is used to estimate the size of crystallites in X-ray diffraction patterns. However, it is often mistakenly referred to as the "Debye-Scherrer equation," which does not exist. Scherrer and Peter Debye collaborated in the early 20th century to develop methods for analyzing crystal structures using fine powder samples, aiming to avoid the need for large single crystals. Their method, the Debye-Scherrer method, was independently developed by Albert Hull. Scherrer's equation, D_hkl = Kλ/(B_hk cosθ), calculates crystallite size based on peak width and Bragg angle. The factor K depends on crystallite shape and peak width definition. K is typically approximated as 0.9 when detailed shape information is unavailable. The equation is limited to crystallite sizes up to about 100–200 nm due to peak broadening limitations. Improvements to the equation involve refining K based on factors like experimental resolution and crystallite shape. The Scherrer equation is named after Paul Scherrer, who was honored by the establishment of the Paul Scherrer Institute. Debye is remembered for his contributions to dielectric and solid-state physics. The authors emphasize the importance of correctly citing Scherrer's 1918 paper and understanding the limitations of the equation.The Scherrer equation, derived by Paul Scherrer in 1918, is used to estimate the size of crystallites in X-ray diffraction patterns. However, it is often mistakenly referred to as the "Debye-Scherrer equation," which does not exist. Scherrer and Peter Debye collaborated in the early 20th century to develop methods for analyzing crystal structures using fine powder samples, aiming to avoid the need for large single crystals. Their method, the Debye-Scherrer method, was independently developed by Albert Hull. Scherrer's equation, D_hkl = Kλ/(B_hk cosθ), calculates crystallite size based on peak width and Bragg angle. The factor K depends on crystallite shape and peak width definition. K is typically approximated as 0.9 when detailed shape information is unavailable. The equation is limited to crystallite sizes up to about 100–200 nm due to peak broadening limitations. Improvements to the equation involve refining K based on factors like experimental resolution and crystallite shape. The Scherrer equation is named after Paul Scherrer, who was honored by the establishment of the Paul Scherrer Institute. Debye is remembered for his contributions to dielectric and solid-state physics. The authors emphasize the importance of correctly citing Scherrer's 1918 paper and understanding the limitations of the equation.