Temperature modulated dynamic scanning calorimetry (TMDSC) yields the characteristic length or, correspondingly, the cooperativity of dynamic glass transition of a molecular liquid in nanometer size pores. The TMDSC traces for benzoin isobutylether are not disturbed by structuring effects that are usually observed in standard DSC. The bulk length of about xi(alpha) = 3 nm decreases with decreasing pore diameter below D = 12 nm, down to xi(alpha) = 1.6 nm in D = 2 nm pores. The glass transition temperature decreases concomitantly. This can be understood in the framework of the hindered glass transition.