I measured and weighed an SD card in my camera. I assume they're all the same. Figuring only the fingers and assuming 30 micro" gold thickness, I estimate about $10.90/pound at a $1211 spot. They weigh about 2g each (227 parts/pound) and the plated area is about 0.13 in2.
(.000030 in3 Au/in2)(10.17 tr.oz.Au/in3)($1211/tr.oz.Au)(.13 in2 Au/part)(227 parts/pound) = $10.90/pound:
The units are (in3)(tr.oz.)($)(in2)(parts) divided by (in2)(in3)(tr.oz.)(parts)(pound). Everything cancels out but $/pound.
When using U.S. weights and measures, 10.17 is always the constant for gold in this formula (for Ag, the constant is always 5.5 - Cu is 4.7). It should be noted that the gold thickness number is always the same as the in3 of gold at that thickness - 0.000030" x 1" x 1" = 0.000030 in3.
Below in bold type is the simplified formula for gold in $, inches, and pounds. For different units, such as microns and/or kg, the 10.17 factor would be different, but it is easily calculated. For example, if you were still using inches and wanted the answer in $ per kilogram, the factor of 10.17 would be multiplied by 2.2, the number of pounds per kilogram. A change in currency would not alter the factor but the results would be in the new currency per unit weight. A change from in, in2, and in3 to cm, cm2, and cm3 would require a new factor.
$ value of gold per pound of parts = (thickness of gold expressed in inches) X (10.17) X (gold spot in $/tr.oz.) X (gold surface area per part in square inches) X (number of parts per pound)
I've gone over this a jillion times but I feel that everyone should know this formula. If too confusing, ask specific questions.