Prague is about 3.3 times smaller than Johannesburg.

Johannesburg is approximately 1,644 sq km, while Prague is approximately 496 sq km, making Prague 30.18% the size of Johannesburg.
Tip: This to-scale comparison of Johannesburg vs. Prague uses the Mercator projection, which distorts the size of regions near the poles.
Our free app, MapSize by MyLifeElsewhere — compare any two places, to scale on your mobile device.