The phrase "a fraction of that size" is correct and usable in written English.
It can be used to describe something that is significantly smaller or lesser in comparison to another object or measurement.
Example: "The new model is impressive, but it is only a fraction of that size compared to the original design."
Alternatives: "a small portion of that size" or "a tiny part of that size".
Russian officials say the entire insurgency is a fraction of that size.
The revenues that flow to the UK are a fraction of that size and are fees paid by Google Ireland for services supplied by the UK unit, a set-up that looks back-to-front even if it has received a thumbs-up from HMRC.
Everyone knows about the 10-kilometer-wide asteroid that helped destroy the dinosaurs, but even something a fraction of that size could devastate humanity, says Michael Rampino, an earth scientist at New York University in New York City.
That may sound undesirable for those of us with large Email boxes that are many gigabytes large, but the reMail team has done an excellent job at compressing data for its search index: Cselle says that they've managed to squeeze 100,000 Emails into 500 megabytes (most Email accounts are only a fraction of that size).
Given that it's currently only a fraction of that size and not yet doing any real harm, F-Secure research Patrik Runald argues that the media should be focusing on the other 20,000 new strains of malicious software that appear every day, most of which are more active than Conficker.
The crowd was a fraction of the size of those that assembled in giant rallies across Texas and Ohio in the past two weeks.
Cygnus is also carrying a telescope that will help to chemically analyse meteors and a prototype exercise station that is a fraction of the size of the equipment currently used by station crew members.
In Japan, Suzuki has shown a hybrid city car that is a fraction of the size of a Toyota Prius.
There are also benefits to driving a car that is a fraction of the size of an Accord.
"Her life consists of extreme loneliness, boredom and isolation in an area that is a fraction of the size of her natural habitat".
Several species feature males that are a fraction of the size of females and exist only to reproduce (the size difference in the blanket octopus is akin to "a human-sized female mating with a male the size of a walnut").
