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Measurements of the star formation activity on cloud scales are fundamentalto uncovering the physics of the molecular cloud, star formation, and stellarfeedback cycle in galaxies. Infrared (IR) emission from small dust grains andpolycyclic aromatic hydrocarbons (PAHs) are widely used to trace the obscuredcomponent of star formation. However, the relation between these emissionfeatures and dust attenuation is complicated by the combined effects of dustheating from old stellar populations and an uncertain dust geometry withrespect to heating sources. We use images obtained with NIRCam and MIRI as partof the PHANGS--JWST survey to calibrate dust emission at 21$\rm \mu m$, and theemission in the PAH-tracing bands at 3.3, 7.7, 10, and 11.3$\rm \mu m$ astracers of obscured star formation. We analyse $\sim$ 20000 optically selectedHII regions across 19 nearby star-forming galaxies, and benchmark their IRemission against dust attenuation measured from the Balmer decrement. We modelthe extinction-corrected H$\alpha$ flux as the sum of the observed H$\alpha$emission and a term proportional to the IR emission, with $a_{IR}$ as theproportionality coefficient. A constant $a_{IR}$ leads to extinction-correctedH$\alpha$ estimates which agree with those obtained with the Balmer decrementwith a scatter of $\sim$ 0.1 dex for all bands considered. Among these bands,21$\rm \mu m$ emission is demonstrated to be the best tracer of dustattenuation. The PAH-tracing bands underestimate the correction for bright HIIregions, since in these environments the ratio of PAH-tracing bands to 21$\rm\mu m$ decreases, signalling destruction of the PAH molecules. For fainter HIIregions all bands suffer from an increasing contamination from the diffuseinfrared background.

Calibrating mid-infrared emission as a tracer of obscured star formation on HII-region scales in the era of JWST