Policymakers and economists are becoming increasingly concerned about wealth inequality. Here we estimate Belgium's wealth distribution — and based on this distribution — the revenue potential, distributional impact, and environmental effect of three proposals for a one-off Belgian wealth tax. Our method consists of (1) estimating the Belgian wealth distribution by extending survey data with a top-tail Pareto distribution based on a novel national rich list, and (2) combining the estimated wealth distribution with proposed tax configurations and published elasticities. There are four main results. First, the wealthiest 1% of households possess ~24% of total net wealth, substantially more than previous estimates suggest. Second, the revenue potential of a one-off tax is considerably higher than estimated by wealth tax advocates. Third, the distributional impact would be limited as the richest 1% of households would still possess at least 23% of total net wealth. Fourth, a one-off tax would likely reduce CO2 emissions by only 0.1–0.6%. Overall, our findings suggest a one-off wealth tax could finance over half of Belgium's COVID-19 costs, but would lead to only small reductions in wealth inequality and environmental impact. Ecological economists may therefore wish to pursue other policy proposals to achieve fair distribution and sustainable scale.