Published article in Pilot and Feasibility Studies: https://doi.org/10.1186/s40814-021-00908-x This project contains information about a pilot study to test an online tool to measure participants’ ideal portion size for a food that can be used remotely as part of an internet survey (a single item without the necessity for a specific keyboard response to move between ‘trials’ for each food). We explored convergent and divergent validity of the online tool based on associations between ideal portion size and predictors of food intake that have been consistently reported (or not) in past research using a previously validated laboratory-based computer assessment of ideal portion size. In the files uploaded to this project page, you will find; an FAQ page about using the tool, the dataset analysed in this project, a demonstration video of the tool in Qualtrics, a how-to video for setting up the tool in Qualtrics, the food photos used in the study, and supplementary materials. The associated pre-registration of this project is linked to on the project homepage. You can also find further information about pilot study 2 which replicated effects of the main study (preregistration, materials, dataset). Link to the OSF Preprint: https://osf.io/qwyuc