A portion of my spreadsheet takes dimensions in inches and calculates area. I believe that it worked at one time but doesn't anymore. The dimensions are formatted to place a " after the number. I have tried the following custom number formats:
##''
#0.000[$'']
0.00\"

They all do a satisfactory job of displaying the numbers but they are not working in my formulas.

For example: cell A1 displays 21". In cell A2 I write the formula =A1*2. Cell A2 displays #VALUE!

How do I get Excel to recognize these as numbers?