With China, the BRICS represent about 25% of nominal global GDP (or as much as 32–36%). Without China, the BRICS represent only about 8.5% of nominal global GDP. China alone accounts for over 65% of the BRICS economy.
Some data on "40% of global GDP" emerges when considering BRICS+ (with new members such as Saudi Arabia, Iran, Egypt, etc.) and using purchasing power parity, which gives more weight to emerging economies.