What amount spinach do you have to eat to get kidney stones?

Spinach and oxalate: Spinach is rich in oxalate; calcium oxalate forms 80% of stones in adults; many foods contain oxalate, only nine foods are believed to promote kidney stone formation. They are: beets, spinach, rhubarb, strawberries, nuts, chocolate, tea, wheat bran, and all dry beans It is best to avoid these foods. Drinking 3 to 4 liters per day of fluid is essential. Too much spinach would be one cup per day