Magnetic Field Calculator

The three formulas each use that number in a physically different role: for the straight wire it's the perpendicular distance r from the wire (B = μ₀I/2πr), for the solenoid it's the coil's total length L used to derive turns-per-length n = N/L (B = μ₀nI), and for the circular loop it's the loop's radius R (B = μ₀NI/2R). Reusing one input field keeps the form simple, but entering a solenoid's length where you meant a loop's radius (or vice versa) will scale the result by whatever ratio those two numbers differ by.

An infinite straight wire has no windings — Ampère's law for it, B = μ₀I/(2πr), depends only on current and distance — so the engine's straight-wire branch never reads the turns value at all. Turns only enters the calculation in the solenoid branch (as part of n = N/L) and the loop branch (as a direct multiplier N in B = μ₀NI/2R).

Raw magnetic field results in tesla are often tiny for everyday currents and distances, so the engine automatically checks the computed field magnitude and rescales it: below 1 μT it displays nanotesla, below 1 mT it displays microtesla, and below 1 T it displays millitesla, always converting the underlying tesla value by the matching power of ten. This keeps the headline number in an easily readable range rather than forcing you to read a string of leading zeros.

Earth's own field at the surface is roughly 25–65 μT, which the explainer text calls out for scale. A solenoid or wire carrying an ordinary current at a reasonable distance often lands in the same μT-to-mT range, while a tightly wound solenoid with many turns and a short length can reach much higher milliteslas — comparing your result against that 25–65 μT benchmark is a quick sanity check on whether an input like distance or turns was entered in the wrong unit.