Western Sahara is about 1.5 times bigger than Oklahoma.

Oklahoma is approximately 177,847 sq km, while Western Sahara is approximately 266,000 sq km, making Western Sahara 50% larger than Oklahoma. Meanwhile, the population of Oklahoma is ~3.8 million people (3.1 million fewer people live in Western Sahara).
Tip: This to-scale comparison of Oklahoma vs. Western Sahara uses the Mercator projection, which distorts the size of regions near the poles.