Calibrating a capacitive moisture sensor
There's not going to be an equation online for you to just plug in your values, as it's going to depend on your specific device, how you're measuring the capacitance, and probably even the wood you're using. Instead, you're going to need to calibrate it yourself, so you'd collect a bunch of points at known moisture values (ex. 0%, 10%, 20%, ...) and measure the capacitance for each. Assuming they form a smooth curve, you can then interpolate between capacitance/moisture values to get your reading