[jman4747]

I dug out my 29th edition of Machinery's Handbook and fond that the calculators the OP is utilizing are the equations on page 2553 of said handbook. The calculator isn't for computing an exact distance based on just the pitch but on an old formula for a "tight" chain. You are supposed to use the bottom calculator first then with the decimal output that it gives for "Links" use the top calculator while replacing the decimal value you got for step one with a close integer value. The result of the top calculator is a "true" exact value and you aren't usually supposed to add anything to it.

See attached equation

Edit: Do what Ed said. That's what this calculator was meant for.