2 X Single Ovens

[batty]

If you are running a cable in then 6mm will cover both ovens. But surely if you are running new circuit in you may as well make it two 16 amp circuits and subject to how cable is run even 2.5 may be adequate. Are you competent to do this work. There is a lot more to designing a circuit its not just picking a cable and circuit breaker. Will circuit need RCD protection ETC.