Process for producing organochlorosilanes in a fluidized bed reactor by reaction of a methyl chloride-containing reaction gas with a particulate contact mass containing silicon and a catalyst, wherein the organochlorosilanes have the general formula (CH 3 ) n H m SiCl 4-n-m where n = 1 to 3 and m = 0 or 1, characterized in that - the reactor design is described by an index, K 1 = φ ⋅ V reactor , eff A tot , cooled ⋅ d hyd where φ = fill level of the reactor, V reactor, eff = effective reactor volume [m 3 ], A tot , cooled = sum of cooled surface areas in the reactor [m 2 ], d hyd = hydraulic reactor diameter [m], wherein V reactor, eff is 1.5 to 2400 m 3 and d hyd is 0.1 to 1.5 m; - the constitution of the contact mass is described by an index K 2 = R Si ⋅ B AK ⋅ δ rel d 32 , where B AK = breadth of the particle size distribution of the contact mass [pm], d 32 = particle Sauter diameter [pm], R Si = purity of the silicon, δ rel = relative catalyst distribution in the contact mass, wherein δ rel is 0.001 to 0.6, d 32 is 5 to 350 μm, B AK is 10 to 1000 pm and R Si is 0.75 to 0.99999; - the reaction conditions are described by an index K 3 = u L ν F ⋅ 10 6 ⋅ p diff g ⋅ 1 ρ F , where u L = superficial gas velocity [m/s], ν F = kinematic viscosity of the fluid [m 2 /s], ρ F = fluid density [kg/m 3 ], p diff = pressure drop over the fluidized bed [kg/m*s 2 ], g = acceleration due to gravity [m/s 2 ], wherein p diff is 10 000 to 200 000 kg/m*s 2 , u L is 0.002 to 0.4 m/s, ρ F is 1 to 5 kg/m 3 and ν F is 3*10 -6 to 2.5*10 -5 m 2 /s; and wherein K1 has a value of 1 to 30, K2 has a value of 0.0005 to 2 and K3 has a value of 0.2 to 3000. - the reactor design is described by an index, K 1 = φ ⋅ V reactor , eff A tot , cooled ⋅ d hyd where φ = fill level of the reactor, V reactor, eff = effective reactor volume [m 3 ], A tot , cooled = sum of cooled surface areas in the reactor [m 2 ], d hyd = hydraulic reactor diameter [m], wherein V reactor, eff is 1.5 to 2400 m 3 and d hyd is 0.1 to 1.5 m; φ = fill level of the reactor, V reactor, eff = effective reactor volume [m 3 ], A tot , cooled = sum of cooled surface areas in the reactor [m 2 ], d hyd = hydraulic reactor diameter [m], wherein V reactor, eff is 1.5 to 2400 m 3 and d hyd is 0.1 to 1.5 m; - the constitution of the contact mass is described by an index K 2 = R Si ⋅ B AK ⋅ δ rel d 32 , where B AK = breadth of the particle size distribution of the contact mass [pm], d 32 = particle Sauter diameter [pm], R Si = purity of the silicon, δ rel = relative catalyst distribution in the contact mass, wherein δ rel is 0.001 to 0.6, d 32 is 5 to 350 μm, B AK is 10 to 1000 pm and R Si is 0.75 to 0.99999; B AK = breadth of the particle size distribution of the contact mass [pm], d 32 = particle Sauter diameter [pm], R Si = purity of the silicon, δ rel = relative catalyst distribution in the contact mass, wherein δ rel is 0.001 to 0.6, d 32 is 5 to 350 μm, B AK is 10 to 1000 pm and R Si is 0.75 to 0.99999; - the reaction conditions are described by an index K 3 = u L ν F ⋅ 10 6 ⋅ p diff g ⋅ 1 ρ F , where u L = superficial gas velocity [m/s], ν F = kinematic viscosity of the fluid [m 2 /s], ρ F = fluid density [kg/m 3 ], p diff = pressure drop over the fluidized bed [kg/m*s 2 ], g = acceleration due to gravity [m/s 2 ], wherein p diff is 10 000 to 200 000 kg/m*s 2 , u L is 0.002 to 0.4 m/s, ρ F is 1 to 5 kg/m 3 and ν F is 3*10 -6 to 2.5*10 -5 m 2 /s; u L = superficial gas velocity [m/s], ν F = kinematic viscosity of the fluid [m 2 /s], ρ F = fluid density [kg/m 3 ], p diff = pressure drop over the fluidized bed [kg/m*s 2 ], g = acceleration due to gravity [m/s 2 ], wherein p diff is 10 000 to 200 000 kg/m*s 2 , u L is 0.002 to 0.4 m/s, ρ F is 1 to 5 kg/m 3 and ν F is 3*10 -6 to 2.5*10 -5 m 2 /s; <EOS>