In China, a picul was 1331/3 pounds. I'm only guessing, but I'll bet that the complete Webster 1913 definition is "In Borneo it is 135 pounds." Literally, a picul was supposed to be the maximum amount that a man could carry on his back.
Source:
Sherman, Julie. "Silk in China circa 1840". http://www.smith.edu/hsc/silk/Papers/julie.html, ?.