Storm water runoff in urban areas will be collected in storm water systems and one typeof solution to receive a flow and pollution reduction is storm water ponds. This studyincludes a literature study that compiles knowledge and literature about storm water andtreatment of storm water by ponds. Compiled information and equations describingrunoff and processes in storm water ponds have been used as base for creating an Excelbased calculation tool specific for storm water ponds. By entering information about astorm water pond as input to the tool step by step it provides an estimated resultregarding the pollution reduction efficiency of the incoming storm water. The toolestimates the reduction efficiency for suspended soils (SS), phosphorus, (P), copper(Cu) and zinc (Zn). The reduction efficiency of SS is determined in the tool by usingtwo different methods that includes input data of the pond hydraulics depending on itsdesign, incoming concentration of SS and the pond volume relative to runoff area. Thetool also estimates the reduction efficiency of SS by particle fraction. Reduction of P,Cu and Zn is estimated in two methods by using the particle bound and the reductionefficiency of SS. The created tool has thereafter been applied on six well documentedponds located in Sweden. The estimated results by the tool is thereafter compeered tothe documented results regarding incoming flow, pollution concertation and reductionefficacy. The estimated tool is also compared with results from StormTac, which is aprogram for design of storm water facilities. The result indicates that the tool estimatesthe incoming flow and concentration relatively well but that it is complicated toestimates the big variations in storm water. Both the tool and StormTac generallyestimates lower reduction efficacy of SS than the actual for all selected ponds. Thereduction efficiency of P, Cu and Zn is also underestimated by the tool compared to theactual values. However, it can be observed that the estimated result follow the sametrend as the actual values and result from StormTac.