Protein per 100g of soy beans: ~40g raw, ~30g cooked
PDCAAS for beef (Protein Digestibility Corrected Amino Acid Score): 0.92
PDCAAS for soy: 0.91
Approximately no additional grams, if you pick the right legumes.
Sources:
https://en.wikipedia.org/wiki/Protein_quality
I eat a high protein, vegetarian diet optimised for lifting weights, and "Approximately no additional grams, if you pick the right legumes." doesn't really add up for me. For the main sources of protein I usually try to eat daily:
Tofu 400g; eggs 3 large; cottage cheese (low-fat) 300g; greek yoghurt (0% fat) 250g; beans/lentils (mixed) 1-3 cans;
and then also supplement with whey protein powder to get to my daily protein target (~150g). To get there with just legumes I'd need to consume 15 cans of cooked lentils (i.e. not achieveable in reality).
Tempeh, seitan (gluten), and TVP are the other protein dense staples of a plant based diet.
They are just alien to Americans.
Soy beans pre-cooked in cans don't exist in the UK.
I don't know if you have checked out black gram, aka urad dal or urid dal. It is used with rice in the batter for idli and dosa in a 1:3 ratio.
high in protein.