Here is a bit of info i found while scrounging around on wikipedia hopes this helps on the sizing, as this is the same size as the one put on the legendary plaque.
The Combat Knife (UNSC CQCWS) is a United Nations Space Command infantry-sized knife.
The multi-purpose combat knife has a 20 centimeter (8 inches) blade made of high carbon steel coated for corrosion resistance and is 43.3 centimeters (1 foot, 5 inches) sheathed.
Sandler
The Combat Knife (UNSC CQCWS) is a United Nations Space Command infantry-sized knife.
The multi-purpose combat knife has a 20 centimeter (8 inches) blade made of high carbon steel coated for corrosion resistance and is 43.3 centimeters (1 foot, 5 inches) sheathed.
Sandler