Drag loads to aquaculture nets are largely determined by the net solidity. Recent years the methodology for measurements of solidity has been more settled with photographical determination of solidity being the preferred method as described in NS 9415 (2021). The amount of empirical data for drag loads to nets have increased, (e.g Føre et al 2022). This has given the possibility for a revisit to the load formulation for drag loads to net membranes in AquaSim (Aquastructures 2013) which is based on Berstad et al (2012). Recent years, wind turbine calculations have been introduced to AquaSim (Aquastructures 2024) based on the BEM method (e.g Hansen 2008). This is based on 1D momentum theory which describes flow through a porous section. The paper presents how 1D momentum theory is combined with the drag formulation from Berstad et al (2012) to update the expression for drag to nets. The momentum theory also leads to an expression for flow reduction behind nets which is an update of the current calculation of flow reduction based on Løland (1991). Comparison to empirical data is carried out and results are discussed. References Aquastructures (2013) “The AquaSim Package Theory User Manual” Aquastructures, Kjøpmannsgata 21, Trondheim, Norway. https://aquasim.no/files/documentation/Theory_manual.pdf Aquastructures (2024) “Calculation of loads on turbine blades using BEM theory”. Aquastructures, Kjøpmannsgata 21, Trondheim, Norway. https://aquasim.no/resources/documentation.html Berstad, A. J., Walaunet, J., and Heimstad, L. F., (2012). “Loads from currents and waves on net structures”. 27th International Conference on Offshore Mechanics and Arctic Engineering, June 15-20. Rio, Brazil Føre, Heidi Moe, Per Christian Endresen & Hans V. Bjelland (2022) "Load Coefficients and Dimensions of Raschel Knitted Netting Materials in Fish Farms" Journal of Offshore Mechanics and Arctic Engineering AUGUST 2022, Vol. 144 / 041301-1. Hansen, M. O. (2008). Aerodynamics of wind turbines. ISBN-13: 978-1-84407-438-2008 Løland, G., (1991). Current Forces on and Flow Through Fish Farms. Doktor ingeniøravhandling: Norges Tekniske Høgskole. Division of Marine Hydrodynamics, the Norwegian Institute of Technology Standard Norway. NS 9415:2021: Floating fish farming installations – Requirements for design, dimensioning, production, installation, and operation. Lysaker: Standard Norway; 2021.