1 cup?! How big is it? 100 ml?!
One cup is about 235 ml, but it doesn't matter. What matters is the ratio of simple green crystal to water.
1 to 8 or 1-10 works well for heavy cleaning, 1-10 to 1-30 works well for medium cleaning and degreasing, and 1-30 to 1-50 works well for light cleaning and degreasing.
I use 1-8 for ultrasonic cleaning.
I use 1-30 for any subsequent O2 cleaning of regulators, valves and tanks.