While some people of the same height may have long legs and short torso lengths, others have
a long torso and shorter legs. . . so, a person's overall height is not all that accurate in determining backpack fit .

~~~ It is best to determine your TORSO LENGTH ~~~

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HOW TO MEASURE YOUR TORSO LENGTH:

Measure the length from your 7th vertebrae ... to a point in the small of your back that
is even with the the top of your hipbones.

The 7th vertebrae is the prominent bump on your spine at the base of your neck.
(This is easiest to locate while tipping your head and looking straight down.)

We recommend you use a mummy bag that is at least 10" TALLER than you are.

The stated size (size shown on the tag) on a sleeping bag is usually the "cut size"
of the outer fabrics before the bag is sewn.  
Once it is sewn, the sleeping bag is a bit shorter and narrower.

Consider that the INSIDE measurements of a sleeping bag is less than the outside overall
measurements because of the fill material. 
The thicker the fill material, the smaller the useable inside dimensions will be.

ALSO, Please be aware of the " MAXIMUM GIRTH " on each size of mummy bag.

IF you are more than 60" or so in girth around the shoulders & chest
( or 48 " around the waist area ) the standard size bag will not fit you properly and
may be uncomfortably tight.

NOTE:

If you have NOT used a mummy style sleeping bag before, you will need to be prepared
for a tighter fit than a regular rectangular sleeping bag.

This closer fit is one of the reasons WHY the mummy bags are warmer than rectangular bags
but some Campers find mummy bags a bit confining until they get used to the different feeling.