The International Technology Roadmap for Semiconductors in the 2010s gave an industrial consensus on feature scaling following Moore's Law. A silicon-silicon bond length is 235.2 pm, which means that a 5 nm-width transistor would be 21 silicon atoms wide.
The International Technology Roadmap for Semiconductors in the 2010s, which was based on Moore's Law, provided an industrial consensus on how to scale transistors.  A 5 nanometer wide transistor would have a width of 21 silicon atoms due to the bond length between silicon atoms being 235.2 pm.