Nominally 21mm in diameter and 70mm high.
The active layers of the cell are wound in a spiral. Normally these cells have the lower case as the negative terminal and the top centre as the positive terminal. However, a number of larger cylindrical cells have both +ve and -ve terminals on the top surface.
Image courtesy of Volklec and shows their 21700 5Ah Energy Cell.
For this article we will concentrate on the 21700 format, but we need to note that other sizes of cylindrical cell are available and that opens up different applications. The 46mm diameter 46xx class of cylindrical cells was introduced in a push to reduce cell manufacturing costs for automotive electric vehicles.
The 21700 cell increased the working volume over the 18650 by a factor of >1.4x
21700 => ~21mm in diameter and ~70.0mm long
These dimensions vary between manufacturers.
Using data from the Cell Database we can see that 70g is a good nominal figure for the mass of a 21700 cell.
The 21700 cell by definition should be 21mm in diameter and 70mm high.
Clearly the cell sizes are quite variable.
Plotting the volume lines onto this shows that the cells have a trendline of increasing diameter and hence increasing the volume by up to 10%.
See also: 18650 Cylindrical Cells, Cylindrical Cell Comparison 4680 vs 21700 vs 18650, Molicel’s 21700 High-Power Roadmap, Single Side 21700 Busbars