Cross-laminated timber (CLT) is increasingly used in medium-rise timber buildings, among other reasons for cost effectiveness and robustness. This paper presents a simple design model using the effective cross-section method for the structural fire design, i.e. the determination of the mechanical resistance with respect to bending (floors). Performing advanced calculations for a large number of lay-ups of various lamination thicknesses, using the thermal and thermo-mechanical properties of wood, charring depths and the reduction of bending resistance of CLT were determined as functions of time of fire exposure. From these results zero-strength layers were derived to be used in the design model using an effective residual cross-section for the determination of mechanical resistance. The model also takes into account different temperature gradients in the CLT in order to include the effect of slower heating rate when the CLT is protected by insulation and/or gypsum plasterboard. The paper also gives results from fire-tests of CLT in bending using beam strips cut from CLT with adequate side protection in order to achieve one-dimensional heat transfer. Reference tests at ambient temperature were performed to predict the moment resistance of the beams being tested in fire. Both, calculations and tests show that results can be highly dependent on the temperature profile caused by e.g. protection.