Long haul flights account for over half of yearly aviation carbon emissions, while only taking up 6% of the total flights. To reduce the emissions of those flights, hydrogen combustion blended wing body (BWB) aircraft are a promising new technology. A conceptual design tool for hydrogen BWB aircraft is created to evaluate the effects of the cabin design and hydrogen tank placement on the aircraft level performance of the concepts. It is found that for a 350 passenger BWB concept a narrow cabin with 45% of the fuel placed next to the cabin results in the lowest fuel burn. For a 250 passenger BWB concept a narrow cabin with 40% of the fuel next to the cabin offers the lowest fuel burn.  The spread in performance is lower for the 250 passenger concepts than for the 350 passenger concepts, indicating the internal layout has a larger effect on the performance of the 350 passenger concepts. Optimising cruise conditions resulted in high optimal altitudes due to the low wing loading of LH2 BWBs, however limitations of the model with respect to the cruise altitude reduce the certainty of conclusions drawn. Conclusions drawn with respect to the sensitivity of the performance to design parameters are limited by uncertainty in the wave drag estimation of the concepts.