Crystal load capacitor calculator
The two caps your crystal actually needs — from its rated CL and your board's strays.
Strays are the traces + MCU pin capacitance — typically 2–5 pF on a tight layout. The datasheet CL is on the crystal's page, usually 8–20 pF.
The circuit this computes
Crystal + Load Caps — fully explained →How it works
A crystal is cut to resonate at its marked frequency only when it sees its rated load capacitance, CL. The two load caps are in series from the crystal's point of view, with board strays in parallel: CL = (C1·C2)/(C1+C2) + Cstray. With equal caps that inverts to C = 2 × (CL − Cstray) — what this calculator computes.
Common questions
Usually the oscillator still runs — just off-frequency (the crystal is 'pulled'), which shows up as UART garbling, USB enumeration failures, or RTC drift. Too-wrong values can also stop it starting at temperature extremes. It rarely fails on the bench, which is exactly why it ships broken.
The two caps are in SERIES as seen by the crystal, so two 22 pF parts present 11 pF, plus a few pF of board strays ≈ 12.5–15 pF. The caps being nearly double the rated CL is correct, not a typo.
You estimate: 2–3 pF for a tight layout next to the MCU, 4–5 pF for longer traces. MCU oscillator pins add ~1–3 pF each (datasheet). Get it within a picofarad or two and the pull is parts-per-million — good enough for everything except radio timing.