Since KPI is a ‘metric’ and a metric can be a number or ratio, we can have KPIs in the form of numbers and ratios. So we can have ‘number KPIs’, and we can have ‘ratio KPIs’. Example of number KPIs: 'days to purchase', 'visits to purchase', 'revenue' etc. Example of ratio KPIs: 'conversion rate', 'average order value', 'task completion rate' etc