The cooking capacity of a wall oven is more dependent on the oven's internal capacity than its exterior dimensions. Different models of 26-inch oven have widely varying actual capacities, ranging anywhere from 1.6 to over 4 cubic feet.
The actual internal capacity of a 26-inch wall oven is affected by many features, such as if the oven includes a integrated microwave or warming drawer. The best way to determine how much capacity that is actually needed for the oven is by the number of people that need to be regularly fed in a household. Approximately a cubic foot of cooking space is required in an oven to cook for each person in a home.