A method (45) for determining the total pressure in a cylinder (Pcyl) of an engine as a function of the angular position (crk) of a crankshaft (14) and from a quantity of fuel to be injected in possibly several injections, includes: determining the pressure in the cylinder when there is no combustion, the pressure being called the pressure without combustion (Pcyl_m), determining, for each injection (inji), a curve of sub-variation of pressure (ΔPcomb_i) caused by the combustion of the fuel quantity injected during the such injection (inji), the shape of the curve being estimated as a function of the quantity of fuel to be injected (MFi) and of the angular position for start of injection (SOIi) of the corresponding injection, determining the total pressure in the cylinder (Pcyl) by adding together the pressure without combustion (Pcyl_m) and the pressures given by the pressure sub-variation curves (ΔPcomb_i) of each injection (inji).