# PDN / Decoupling Planner > From a power rail's target impedance get the decoupling network: bulk, HF capacitors and ripple margin. Practice: elettronica Status: Proto v0.1 Tag: PDN, Decoupling, Power integrity, Condensatori, Impedenza Method, assumptions and limits: Page: --- Demonstrative tool for sizing a rail's decoupling. From the allowed voltage ripple and the transient switching current it computes the target impedance Zt = ΔV/ΔI; based on Zt and the maximum frequency of interest it suggests a decoupling network (bulk capacitance + HF capacitors, indicative count and values) to keep the impedance magnitude below Zt, with an estimate of the bulk-to-HF antiresonance frequency. This file is a **descriptor**, not the tool's documentation: it says what the tool computes and by what method, in summary. Formulas, assumptions, validity conditions and limits are in the wiki linked above. The tool runs in the browser at the page given.