Field mapping devices are used to determine the spatial distribution of magnetic fields. As magnetic devices are very unique in shape and size, commercially available mapping devices are often complex and customised and therefore too costly for small-format magnetic resonance imaging (MRI) systems and the open-source community. A low-cost field mapping device with a Hall sensor for the OCRA tabletop MRI system1 is developed. Field maps are measured and compared against a commercial Hall probe. The presented measurements show that the developed device can compete with commercially available devices.