Function line_height_px 

pub fn line_height_px(size: f32, text_scale: f32) -> f64

Height of one line of size-pt text at text_scale without a renderer in hand — exactly what crate::text_render::TextRenderer::measure reports for a single line, size × text_scale × line_height of the legacy TextStyle.

Widgets that paint have a renderer and use the .1 of measure*; this is for the layout passes that solve a row grid before any paint (an app’s build_layout / measure, a metrics struct built from the theme) and must agree with what paint will measure. One owner for the formula, so the apps stop carrying size × 1.25 copies.