The heat output of a stove is measured in Kilowatts (kW).
The size of your wood-burning stove depends on the size of the area you wish to heat.
A stove that is too large can cause just as many problems as a stove that is too small, as if it is too big for the room, you will be forever cutting the air supply to keep the room temperature down. As a result, combustion will be incomplete and soot will quickly build up on the stove window and in the chimney. In addition, the quantity of soot particles you emit into the environment will be disproportionately high.
A draughty Victorian house clearly needs more heating power than a well insulated, double glazed modern house. For the former, a calculation based on 1kW of heat per 10 cubic metres of space would allow for contingent heat loss while for the highly insulated modern new build might require as little as 1kW of heat per 25 cubic metres of space.