The ability of noble metal nanoparticles (NPs) to convert light into heat has triggered a lot of scientific interest due to the numerous potential applications, including, e.g. photothermal therapy or laser-based nanopatterning. In order for such applications to be practically implemented, the heating behaviour of NPs embedded in their surrounding medium has to be thoroughly understood, and theoretical models capable of predicting this behaviour must be developed. Here we propose a multiscale approach for modelling the photothermal response of a large ensemble of nanoparticles contained within a cm-scale, real-size container. Electromagnetic field, ray tracing and heat transfer simulations are combined in order to model the response of nanostars and nanospheres suspensions contained within a common Eppendorf tube. To validate the model, gold nanostars are then synthesised and characterized by electron microscopy and optical spectroscopy. Laser-induced heating experiments are conducted by irradiating colloid-filled Eppendorf tubes with a 785 nm continuous wave laser and monitoring by a thermographic camera. The experimental results confirm that the proposed model has potential for predicting and analysing the heating efficiency and temperature dynamics upon laser irradiation of plasmonic nanoparticle suspensions in real-scale containers, at cm3 volumes.