This is the purpose of historical materialism. This is what everything’s been about. Let’s get to it. 

Alright I googled “Vladimir Lenin height and weight” and got directed to this guardian article. Assuming this information is true (I know, it’s The Guardian), Lenin was 5’5”, 165 lbs. I tried googling for Marx’s height/weight but didn’t find any direct results. However, one Yahoo Answers user described him as being of “average height” and referred to this website which posted the following quote: 

Marx greatly impressed as all. He was of medium height, broad-shouldered, powerful in build, and vigorous in his movements. His forehead was high and finely shaped, his hair thick and pitch-black, his gaze piercing. Marx was a born leader of the people. His speech was brief, convincing and compelling in its logic. He never said a superfluous word; every sentence contained an idea and every idea was an essential link in the chain of his argument.

So Marx was definitely medium height. We should then be able to reasonably infer his height from looking at whatever that medium height was, right? According to these definitely infallible statistics provided by ChaCha, the average height and weight for a man in the 1840’s was 5’6” and 140-160 lbs. So let’s say Marx was 5’6” and 160. He has an inch on Lenin, but concedes five pounds. What’s more significant here? Is an inch worth more or less than five pounds in weight? I can’t answer this right now, I’m only on the second chapter of Capital. 

Here’s a description of Lenin on his wikipedia article: 

Concerned with physical fitness, he took regular exercise,^[243] enjoyed cycling, swimming, and shooting,^[244] also developed a passion for mountain walking in the Swiss peaks.

So Lenin kept in shape. 

Unfortunately, “broad-shouldered and powerful in build” is much vaguer than that. I do feel comfortable asserting that Lenin would definitely win a fight against Marx with a gray beard. Young Marx vs Prime Lenin would be a good contest.

But here’s what really matters: Mao was 5’10” and 190 (according to this site which otherwise just slanders him) and worked on his father’s farm in youth, walked a shit ton and loved to swim. He has 4/5 inches and 25/30 pounds on them. Mao would wreck them both and this is why Maoism is the necessary development of Marxism-Leninism.