EMBEDDED TOOL
Crystal Oscillator Load Capacitance Calculator
Find crystal load capacitance from C1/C2, or matched C1/C2 from a target CL.
Load capacitance
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About this tool
Calculate the effective load capacitance seen by a crystal oscillator from its two external capacitors (C1, C2) and PCB/pin stray capacitance — or work backward from the crystal's datasheet load capacitance (CL) to find matched C1/C2 values, the most common design task when picking crystal load caps.
Frequently asked questions
- What's the formula?
- CL = (C1 × C2) / (C1 + C2) + Cstray — the two capacitors appear in series as seen by the crystal, plus whatever stray capacitance the PCB traces and IC pins add.
- Why use equal C1 and C2 values?
- Symmetric C1 = C2 is the standard choice for a balanced oscillator circuit, keeping the two crystal pins' loading even — this tool's "Find matched C1/C2" mode assumes that symmetry when solving backward from CL.
- What's a typical stray capacitance value?
- 2–5pF is a common estimate for combined PCB trace and microcontroller pin capacitance, though it varies by layout — check your MCU's datasheet for a more precise figure if the oscillator needs to be accurate.