calculation is to use a ratio of capital expenditure to sales over multiple past years. As formulated by Greenwald, this approximation works by:

# Sum of property, plant, and equipment (PPE) from the balance sheet for the past 5 years
# Sum sales from the income statement for the past 5 years
# Dividing the sum of PPE by the sum of sales to find the average ratio of PPE-to-sales
# Multiply the PPE-to-sales ratio by the nominal increase or decrease in sales from the prior year to the current year to find growth capital