A filter for use in a storm water drain to prevent debris from reaching the outlet of the drain. The filter is adjustable to be sized for a range of flow capacities. The filter includes a main filter section having openings through which water flows. A pair of adjustable side grates project from the main filter section and are adaptive to be connected to the sidewall of a storm drain. Flow capacity of the filter can be varied by adjusting the effective width of the respective side grates.