What is the length of wire needed to create this spring?

So I model the spring:

I then create a helix that runs through it entirely.  Figure it intersects any quadrant on the starting-bottom circular face and it will intersect the same quadrant on the finishing-top circular face; thing left to left, top to top, center to center.  Measure that helix and you get:

Arc Length = 28.11"

Another method might be to evaluate the volume of the modeled spring and reverse-solve for the length:

where the volume of the above model is  π = 3.14..., r is the radius of the wire (0.0625") and h is the length

0.33720901=π(.0625)²h; h=0.33720901/(π(.0625)²) = 27.48"

Another method might be:

where π = 3.14..., c= number of coils/turns, D = outer diameter (1") and d = wire diameter (.125") giving you:

10π(.875) = 27.49"

It's interesting that the last two numbers differ, I imagine because of rounding error.  What I don't understand is why does my perfectly-aligning helix not measure the same?  It must be fundamental I don't understand about Arc-Length 

Is there a method, maybe using surfaces or sheet-metal, to flatten this out to measure?  The math gives me a different number.  I could imagine a scenario where I'm making a million springs and end up a few hundred feet short of wire based on SolidWorks' measurement.