Citizen science has long been used as an approach across different disciplines, both in terms of the science produced, and the democratisation of the process to involve all stakeholders that have a vested interest. However, whilst citizen science’s potential to contribute towards such concerns is well documented, limitations exist when measuring the impact that citizen science has made. Despite multiple attempts across the literature, there remains no formal process by which to assess a citizen science project’s impact and to accurately compare that impact with other projects, traditional science, or the status quo. The MICS (Measuring the Impact of Citizen Science) project has developed an online platform and toolbox that citizen-science project coordinators can use to assess the impact of their activities, whilst generating comparable results across the citizen science landscape. MICS considers impact across five domains (environment, society, economy, governance, and science and technology), and consists of approximately 200 indicators - implemented in the form of questions - designed to find out as much information as is possible about a project’s intended or achieved impact across these domains. These 200 indicators have been generated and refined through a combination of literature reviews, workshops and iterative interviews to capture as much information about impact as possible. The MICS platform and assessment-approach have been demonstrated to a number of project coordinators from a range of projects. In this work, we present the design of the platform, and demonstrate its relevance to citizen science, and suitability for measuring its impact.