ΔE 6.9, close: similar, with a visible difference side by side. USAAF Light Gray is a little lighter, warmer than Gray FS26440.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). USAAF Light Gray is a little lighter, warmer than Gray FS26440.
The same difference applies the other way round: Gray FS26440 is a little darker, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Gray FS26440 on the colour wheel See USAAF Light Gray on the colour wheel
All matches: Gray FS26440 equivalents · USAAF Light Gray equivalents