There have been some studies on the measurement of tax progressivity since the innovative works of Suits (1977) and Kakwani (1977). These measurements essentially rely on the idea of the Lorenz distribution of income and tax burden and the Gini concentration of inequality. Instead of such a traditional idea, this paper proposes a new measure of tax progressivity based on the relative volatility of tax revenue vis-a-vis income. The advantage of our approach is to make it possible to assess the degree of tax progressivity and to do international comparisons without any specific information about the distribution of the income and tax burden. All we need is macro data, which is a lot easier to obtain than micro data. This paper also discusses some international comparisons using the new measurement.