As long as your numbers fit in that =hex2dec() and =dec2hex() ranges:

=DEC2HEX(HEX2DEC(A1)+HEX2DEC(A2))

I don't know of anyway of using a custom format to display hex.

Dave wrote:

Hi,
As the subject states, how do I add together cells containing hex numbers. I
tried
the following...

A1 contains 0f
a2 contains 0f
a3 contains = a1 + a2
result #VALUE!

I know that it knows the cells could be hex because if I do =hex2dec(a1) in
another cell it converts it. Is there anyway in Excel to explicitly set the
number type of a cell?

Regards,
Dave.

--

Dave Peterson