BACKGROUND: The foot posture index (FPI) is a commonly used method to quantify standing foot posture. No normative data have, however, been presented to establish the range of a normal difference and asymmetrical differences between FPI score in the right foot and in the left foot. PURPOSE: The purpose of the present study was to establish normative values for the difference between the FPI scores across the two feet. METHODS: Among 930 healthy adults, FPI score was quantified in both feet. Difference between the two feet was calculated as FPI score on the right foot minus the FPI score on the left foot. Based on a normal distribution of the differences, asymmetry was defined as values below or above one standard deviation (SD) from the mean. Severe asymmetry was below and above ±2SD from the mean. Normal difference was defined as the range between ±1SD. RESULTS: A reference range for normal difference in FPI score between left foot and right foot was -2 to +2. Asymmetry scores ranged from -2 to -4 and +2 to +4, while severe asymmetry was 4. CONCLUSION: Normative values for the difference between FPI scores in right foot and left foot have been presented from a large sample of healthy adults. These normative values can be used to identify a normal difference or an asymmetrical difference in foot posture across feet in one individual.