Disclosed are techniques for sizing wearable items by device scanning. A shopper scans a wearable item with a sensor assembly of a mobile computing device, such as a mobile phone. A wearable-item mapping is generated based on the scan of the wearable item. Similarly, a body part of the shopper is scanned with the sensor assembly to generate a body-part mapping based on the scan of the body part. The wearable-item mapping is then be compared to the body-part mapping, and a fit result determined based on the comparison. The fit result indicates for the shopper whether or not the wearable item is compatible with an associated body part and likely to fit the person. The fit result is presented at the mobile computing device, such as via an audio feedback or a visual feedback.