The Philadelphia Mindfulness Scale (PHLMS) is a 20 item measure consisting of 2 sub-scales (acceptance and present moment awareness).
Reference:
Cardaciotto, L., Herbert, J. D., Forman, E. M., Moitra, E., & Farrow, V. (2008). The assessment of present-moment awareness and acceptance: The Philadelphia mindfulness scale. Assessment, 15, 204-223.