This might be a bit more involved than you need, but here is the Pans Ops Radius of Turn formula that I use :-
Cell numbers are different from those mentioned previously, as follows :-
D2 = TAS value
F2 = Angle of bank.
Result is in NM
To convert IAS to TAS, the Pans Ops formula is :-
A2 = IAS value in NM/Hr
B2 = Altitude in Feet
C2 = Variation from ISA
Note that this formula and calculation is a prerequisite to the Pans Ops radius of turn formula and calculation.
Theoretically, the wind should be taken into account, to determine the total airspace needed to complete the turn. As an example, using the above formulae in conjunction, I made calculations for 280 and 400 knots at 10,000 feet, IAS +15, at 25 degrees AOB.
Radius at 280 KIAS = 3.507 NM with wind effect at 0.494 NM per minute of turn. The airspace used in the first 90 degrees of the turn is 4.646 NM.
Radius at 400 KIAS = 7.170 NM with wind effect at 0.706 NM per minute of turn. The airspace used in the first 90 degrees of the turn is 8.761 NM.
The total area for the first 90 degrees of the turn includes an allowance for distance travelled between the time the bank is applied and the aircraft begins to turn.