Ok Bob, then the Arm and Hammer is likely Na2CO3.H2O or 105.66 + 16 = 121.66 therefore the total using all Arm and Hammer would be 121.66 /105.66 or 1.15 x more Arm and Hammer to equal your pure anhydrous stuff.

That is, provided that the Arm and Hammer is a monohydrate. If the box does not tell you, check their web site or the MSDS for it.