ΔE 9.7, close: similar, with a visible difference side by side. IJA Light Grey Green is a little darker, warmer than Gray FS16440.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). IJA Light Grey Green is a little darker, warmer than Gray FS16440.
The same difference applies the other way round: Gray FS16440 is a little lighter, 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 FS16440 on the colour wheel See IJA Light Grey Green on the colour wheel
All matches: Gray FS16440 equivalents · IJA Light Grey Green equivalents