Background. Wound measurements are essential to effective wound management and should be recorded every time a wound is assessed. The move towards evidence-based practice to achieve optimal treatment outcomes, cost effectiveness, and reductions in antibiotic use demands more objective, reliable assessment tools and documentation to allow treatments to be compared through an accurate interpretation of results. Today, smart phones are commonplace and their high-quality photography could allow significantly improved accuracy and reliability of wound measurements. Objective. The purpose of this prospective study is to test the reliability of wound surface area measurements using a smartphone application versus the current gold standard (ruler method). Both interrater and intrarater reliability were tested. Materials and Methods. Twenty-five volunteers (raters) of varying clinical experience measured a set of 12 photographs composed of various sizes and shapes of wounds. Each rater measured the same set of photos twice on day 1: once using a ruler and then using the smartphone app. Each rater then repeated these 2 measurements on the same set of photos 1 week later. Results. Overall, the ruler method produced wound area measurements that were 30% larger than the app method with the difference tending to be greater for smaller wounds. The resulting intrarater intraclass correlation coefficient (ICC) averaged across all wounds was in the excellent range for both the app and the ruler (ICC, 0.99 for the app; ICC, 0.92 for the ruler), indicating that raters using either method had a high degree of agreement. The interrater reliability using the app was high (ICC, 0.77), showing an excellent level of agreement across raters with the app; however, the ruler was poor (ICC, 0.34), demonstrating a low level of agreement between raters with the ruler method. Conclusions. This study found that the smartphone wound assessment app produced sufficiently consistent results and appears to be superior to the current gold standard of linear measurements with a ruler.