Russia is clearly the larger of the two: about 16,879,701 km² km² against 9,439,424 km² km², roughly 1.8× at true size. Drag one onto the other on the map above to feel the gap.
Russia sits in Europe, United States in North America. On the old Mercator map the latitude gap distorted how large each felt beside the other; at true size the answer is simply 1.8×.
The old map muddied it further: Mercator inflates Russia about 6.1× and United States about 2×, so on a Mercator-style map this pair appears 5.5× apart instead of the true 1.8×.
United States fits 1× into Russia.