At Tritium Laboratory Karlsruhe (TLK) calorimetry is used as the primary method for tritium accountability and for samples ranging from micrograms to tens of grams. An accuracy of 0.3% is achievable for samples containing more than 0.5 mg tritium and the precision of each calorimeter is better than 0.5%. The results of the TLK calorimeters vary within maximum 0.6% from each other.