Depends how accurate you want your measurement:
The number looks like the result of a calculation, so to simplify it, round it to an appropriate number of significant figures: the number being dependant upon what you are measuring and how you measured it - ie what kind of accuracy you used to measure whatever it was in the first place.
reasonable simplifications would be:
It is 16/20 which can be simplified, if required.
144 inches : 2.5 feet = 144 : 30 = 24 : 5
0.31 inches = 31/100 inches and that fraction cannot be simplified further.
0.321 inches = 321/1000 inches. The GCD of these numbers is 1, so the fraction can't be simplified any more.
The ratio of 153 inches to 17 feet is 153:204, or simplified as 3:4.
It is 16/20 which can be simplified, if required.
It is 626/1000 inches, which can be simplified if you so wish.
2 yards and 3 inches.
It is 28/36, which can be simplified, if required.
144 inches : 2.5 feet = 144 : 30 = 24 : 5
0.392 inches is equal to 392/1000 inches. This can be simplified to 98/250 inches.
3 ft 4 inches is 36 in + 4 in = 40 in. The simplified version of 40in is 2sqrt10 inches.
It is 20/36, which can be simplified, if required.
It is 108/8, which can be simplified, if required.
0.31 inches = 31/100 inches and that fraction cannot be simplified further.
0.321 inches = 321/1000 inches. The GCD of these numbers is 1, so the fraction can't be simplified any more.
To convert 0.175 inches into a more understandable fraction, it can be expressed as 175 thousandths of an inch. This is equivalent to 7/40 inches when simplified. Thus, 0.175 inches is a little less than 3/16 inches.