When you need to set a pixel value for something like Paint.setTextSize but still want it be scaled based on the device, you can convert dp and sp values.

DisplayMetrics metrics = Resources.getSystem().getDisplayMetrics();
float pixels = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 12f, metrics);

DisplayMetrics metrics = Resources.getSystem().getDisplayMetrics();
float pixels = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 12f, metrics);

Alternatively, you can convert a dimension resource to pixels if you have a context to load the resource from.

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <dimen name="size_in_sp">12sp</dimen>
    <dimen name="size_in_dp">12dp</dimen>
</resources>

// Get the exact dimension specified by the resource
float pixels = context.getResources().getDimension(R.dimen.size_in_sp);
float pixels = context.getResources().getDimension(R.dimen.size_in_dp);

// Get the dimension specified by the resource for use as a size.
// The value is rounded down to the nearest integer but is at least 1px.
int pixels = context.getResources().getDimensionPixelSize(R.dimen.size_in_sp);
int pixels = context.getResources().getDimensionPixelSize(R.dimen.size_in_dp);

// Get the dimension specified by the resource for use as an offset.
// The value is rounded down to the nearest integer and can be 0px.
int pixels = context.getResources().getDimensionPixelOffset(R.dimen.size_in_sp);
int pixels = context.getResources().getDimensionPixelOffset(R.dimen.size_in_dp);