Approximate Turn Radius formula for an Air Vehicle (plane/missile/etc)

R = V² / A

Where:

R: Turning Radius of air vehicle in meters.
V: Velocity of air vehicle in meters per second
A : Turning acceleration capability of air vehicle in meters/sec².

EXAMPLE

A supersonic anti-ship missile traveling at Mach 1.5 at sea level (510 m/sec) and with a turn capability of 10 gees (98 m/sec²). What is it's turn radius?

510² / 98 = 2,654~ meters.

Source:
Subsonic and Supersonic Anti-Ship Missiles: An Effectiveness and Utility Comparison (Jan. 1997 Naval Engineers Journal)