The official SI (System International – International agreement to use MKS units) Unit of magnetic field strength is the tesla (T). Magnetic field “strength” describes the Magnetic Induction or Magnetic Flux Density: the number of lines of magnetic flux per unit area. The unit of magnetic flux is the weber (Wb); so 1 T = 1 Wb/m2 (or kg × s−2 × A−1), where 1 Weber represents m2 × kg × s−2 × A−1. A conventional unit of magnetic field strength is the Gauss (in cgs units). 1 Tesla (T) = 10,000 gauss. In mathematical equations, the Tesla is used to avoid confusion and errors due to the need for conversion factors. A typical MRI scanner has a field strength of 1.5–3.0 T. Greater field strength allows better resolution. In the USA, 8 T is the maximum magnetic field strength approved by the FDA for clinical use on humans at this time. 11.7 T is available for research purposes in humans and 21.1 T is available for small animal studies.