The critical current forinsituprepared Cu‐Nb3Sn microfilamentary composites has been measured as a function of both temperature and magnetic field in order to determine the suitability of these materials for superconducting magnets which operate above 4.2 K, either continuously or in brief excursions. A rather simple relation,Jc=AB−1/2(Bc2−B)2whereA=860 A cm−2T−3/2, describes the data very well. The temperature dependence ofBc2is the dominant factor controllingJc(T). Values ofBc2determined both from low current resistive transitions and from Kramer plot extrapolations giveBc2=B0(1−t2), whereB0is approximately 19 T. Scaling applies in these materials and the volume flux pinning force goes asB5/2c2as predicted if the flux line shear modulus controls the flux pinning. The data show that a magnet designed to operate at 4.2 K and 12 T also will operate well at 10 K and 7 T.