Engineering CalculatorsGrounding / Bond Strap Inductance Calculator
Self-inductance and impedance of a flat grounding/bonding strap — impedance, not DC resistance, governs how well a bond performs at RF, which is why wide flat straps outperform round-wire pigtails of the same length.
New to Grover/Terman Straight-Conductor Self-Inductance? Read the guide: Grounding Strap Inductance: Why Impedance, Not Resistance, Rules RF Bonding — a plain-language explainer of the standard behind this calculator.
Classical Grover/Terman straight-conductor self-inductance: a flat strap follows L(nH) = 0.2·l·[ln(2l/(w+t)) + 0.2235·(w+t)/l + 0.5] and a round wire follows L(nH) = 0.2·l·[ln(4l/d) − 1] (l, w, t, d all in mm) — both standard textbook results for the external self-inductance of a straight non-magnetic conductor. Impedance, not DC resistance, is what determines a grounding or bonding connection's effectiveness at RF: Z = 2π·f·L grows directly with frequency, so even a short lead can present meaningful impedance well below 100MHz — which is exactly why EMC practice favors short, wide, flat straps over longer or narrower alternatives, and strongly prefers a strap over a round-wire "pigtail" of the same length. This is the conductor's own self-inductance only — it does not include loop inductance from the return path, joint/contact resistance, or proximity effects from nearby conductors.
Validated: both formulas reproduce the widely-cited EMC rule of thumb that "10cm of ordinary wire has roughly 100nH of inductance, about 63Ω at 100MHz" almost exactly — a 100mm/1mm-diameter round wire gives 99.8nH (62.7Ω at 100MHz), and a comparable 100mm/1mm×1mm flat strap gives 102.2nH, independently confirming both the formulas and their mm-in/nH-out unit convention (a detail several secondary sources reproducing this formula omit). Widening a strap at fixed length and thickness was checked to monotonically reduce its inductance, and impedance was checked to scale exactly linearly with frequency at fixed inductance.