Can I run two cooktops on one circuit breaker?
If you live in the US and your area uses the National Electrical Code then you can run a single circuit and tap off of it to feed the two cooktops. To use this rule though you have to run a 50 amp circuit.
In your case it would be cheaper to run two sparate circuits of 15 amps. Unless the equipment is marked for a higher circuit size. Doing the math on your voltage and power requirements is not a substitute for the manufacturer's recommended circuit size.
According to the NEC:

210.19(3) Household Ranges and Cooking Appliances. Branch-circuit conductors supplying household ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 83⁄4 kW or more rating, the minimum branch-circuit rating shall be 40 amperes.
Exception No. 1: Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units shall have an ampacity of not less than 20 amperes and shall be suffıcient for the load to be served. These tap con-ductors include any conductors that are a part of the leads supplied with the appliance that are smaller than the branch-circuit conductors. The taps shall not be longer than necessary for servicing the appliance.

Good luck!