The Bauer magazine said it experienced a 60% uplift in advertising demand for the issue of the women's weekly for the issue, which goes on sale 20 September.
Such is the demand for the Polestar-printed magazine that the publisher said the backlog meant subsequent issues in September would also be bigger than normal.
Previously the largest edition had been 194 pages, an issue size that could still be stapled.
Grazia managing director Jo Morrell said: "The London Fashion Week edition is a real milestone moment in the development of Grazia, demonstrating a continually increasing demand in the marketplace and underlining Bauer Media's continued investment."
Grazia's ABC circulation figure for the first six months of the year was 219,741.
Grazia makes perfect-bound debut for bumper London Fashion Week issue
Grazia is to produce a special 300-page perfect bound spine - its first ever - for London Fashion Week.
