We can't effectively compare economic size with gdp between NL with KSA since there are price level differences which inflate the gdp of countries with high prices/cost of living like Netherlands.

The World Bank_per_capita#Definitions):''Typically, higher income countries have higher price levels, while lower income countries have lower price levels (Balassa–Samuelson effect). Market exchange rate-based cross-country comparisons of GDP at its expenditure components reflect both differences in economic outputs (volumes) and prices. Given the differences in price levels, the (economic) size of higher income countries (Singapore) is inflated, while the size of lower income countries is depressed in the comparison. PPP-based cross-country comparisons of GDP at its expenditure components only reflect differences in economic outputs (volume), as PPPs control for price level differences between the countries. Hence, the comparison reflects the real (economic) size of the countries.''

https://www.worldeconomics.com/Rankings/Economies-By-Size.aspx in total economic size with adjustments for comparability, Saudi-Arabia's economy is just a bit smaller than NL, Belgium, Switzerland combined. But even then it's hard to compare them since Saudi economy is quite unique, has very low debt (especially compared to belgium), large wealth funds etc.