fit on the back of a postage stamp

fit/write something on the back of a postage stamp

if you say you could write what you know about a subject on the back of a postage stamp, you mean you know very little about that subject What I know about car maintenance could be written on the back of a postage stamp.
See also: back, fit, of, on, postage, stamp
References in periodicals archive ?
What we know about Pluto today could fit on the back of a postage stamp," said Colleen Hartman, a NASA administrator.