This study provides a quantitative assessment of food security using a large household- level expenditure survey conducted by the Government of India during 2004/05. The analysis tests the impact of several key assumptions required to estimate actual calories consumed from the expenditure data. The authors found significant differences in the estimates of calories consumed and the number of food-insecure people under alternative plausible assumptions for computing the calorie content of nonprocessed foods, processed foods, and meals eaten outside the household. The measurement errors were largest in accounting for calories consumed by the highest and lowest income households. Overall, the difference between the highest and lowest estimate of the number of people consuming an average of less than 2,100 calories per day was equivalent to about 17 percent of India’s population, or 173 million people in 2004/05. Given the significant measurement error in estimating calories consumed, it is important to consider not only consumption surveys, but also aggregate food availability studies and survey data on anthropometric measures that accompany undernourishment—such as growth stunting— in assessing food insecurity.