  Metallic coplanar microwave resonators are widely employed at room
temperature, but their low-temperature performance has received little
attention so far. We characterize compact copper coplanar resonators with
multiple modes from 2.5 to 20 GHz at temperatures as low as 5 K. We investigate
the influence of center conductor width (20 to 100 {\mu}m) and coupling gap
size (10 to 50 {\mu}m), and we observe a strong increase of quality factor (Q)
for wider center conductors, reaching values up to 470. The magnetic-field
dependence of the resonators is weak, with a maximum change in Q of 3.5% for an
applied field of 7 T. This makes these metallic resonators well suitable for
magnetic resonance studies, as we document with electron spin resonance (ESR)
measurements at multiple resonance frequencies.
