Thermal capacity, also referred to as heat capacity, is the amount of heat required to change the temperature of an object by a certain degree. On the other hand, specific heat capacity, also referred to as the specific heat of a material, is the amount of heat needed to raise the temperature of an object per unit mass of that object.
From these definitions, we can see that thermal capacity is an extensive property. This means that it varies per amount of the substance. For example, 50 grams of iron will have a different thermal capacity as 100 grams of the same substance. Meanwhile, specific heat capacity is an intensive property. Using the same example, 50 grams of iron will have the same specific heat as 100 grams of iron.
The unit for thermal capacity is J/K (joule per Kelvin) while that of specific heat is J/Kg (joule per Kelvin per gram).
Because of this, thermal capacity is a measurable physical quantity. It is the parameter that can be measured experimentally. Specific heat, on the other hand, is a derived quantity by getting the ratio of the heat/thermal capacity to the mass of the object of interest. Another commonly used parameter is the molar specific heat which is the ratio of heat/thermal capacity with the number of moles (instead of the mass of the object),