I agree with Pommie. The weight and resistance is all the information that is necessary.
The density of copper is 8.96e3 kg/m^3
The resistivity is 1.68e-8 ohm-m
The weight is 2.5 lb = 1.13 kg
The resistance is 80 ohms.
The resistance of a piece of wire is equal to the length divided by cross sectional area times resistivity:
R=L/A*r
The weight is equal to the cross sectional area times the length times the density:
W=L*A*d
You have two equations in two unknowns which can be combined to give:
L=sqrt(W*R/(d*r))
where:
L=Length in meters
W=weight in kilograms
R=resistance in ohms
d=density in kg/m^3 = 8960
r=resistivity in ohm-m = 1.68e-8
Substituting the known info into this formula, you get a length of 776.78 meters, and then using the length to calculate the wire cross section:
A=L*r/R
you get 1.63e-7 m^2 which is equivalent to a diameter of 0.46mm or wire gauge 25 AWG.
For the second coil with the same weight and resistance of 12.2 ohms you get a length of 303 meters and a wire diameter of 0.73mm or #21AWG. This one disagrees with Pommie's calculation, but if the resistance is less for the same weight, then the wire size must be larger, and hence the length must be less.
Edit:
BTW, the formula to convert wire diameter to AWG is:
AWG=36-8.624889* Ln(200*D)
where D is diameter in inches, or
AWG=36-8.624889* Ln(7.874*D)
where D is diameter in mm