what is the volume of duffle bag
According to the manufacturer, the bag measures 71x41x41 cm. The volume (in liters) of such a square box (rectangular prism) is ca 119 liters. The TNF duffel is almost a perfect cylinder, so it's volume is then easy to calculate: 71 x (41/2)^2 x Pi = 93.7 liters according to the manufacturer's measurements.
My TNF Base Camp 90 liter duffel bag has served me well, but most of the time I wished I had a slightly bigger and lighter duffel bag (with similar features). The Patagonia Black Hole 120 liter duffel looked like a good choice - lighter, similar features, and 30 liters of extra space.