Ohmstead: Resistor Calculator

Update guide

Version 2.0 (build 3)

This guide covers version 2.0. The current website catalog lists version 2.0. Check the App Store for availability on your device; the features below require version 2.0 or later.

Keep your electronics calculations, saved scenarios and reference lookups together on iPhone and iPad.

CALCULATE WITH CLEAR INPUTS Use 44 calculators for Ohm’s law, power, dividers, LED resistors, filters, reactance, resonance, timers, op-amp estimates, transmission-line approximations, duty cycles and more. Choose the two known quantities for Ohm’s law and power. Invalid or incomplete inputs are flagged, and each tool explains its model. These are idealized calculations, not circuit simulation or a component safety certification.

SAVE AND REUSE YOUR WORK Save a named calculation with its inputs, unit selections, results and notes. Reopen a calculation saved in this version, adjust the inputs and save a new scenario. Compare saved scenarios from the same calculator. Older text-only bench sheets stay intact as historical snapshots; they are not silently recalculated. Pin favorite calculators to the Bench.

BACK UP AND SHARE Save your complete library as a JSON backup through Files. Restore adds missing sheets, skips identical sheets and stops without changes if an identifier conflicts. Export one sheet or the entire library as readable text, including notes. Backups support up to 2,000 sheets within 20 MB.

DECODE RESISTORS Read 4-, 5- and 6-band resistor color codes, including tolerance and temperature coefficient. Decode 3-digit, 4-digit and EIA-96 SMD markings. Browse E6 through E192 preferred values with representable markings, illustrative color bands and nearest-value comparisons. A nominal value does not establish the tolerance or power rating of a physical part.

LOOK UP REFERENCE INFORMATION Search 231 part/function entries, with 45 selected manufacturer-specific pin references. Filter to pin references and open their source documentation. Generic entries do not claim universal package pinouts or electrical ratings. Browse 31 connector references, 51 formulas, capacitor codes, AWG geometry and resistance, ideal reactance tables, SI prefixes and decibel ratios. Related-part lists are research leads, not guaranteed substitutes. PCB trace-width estimates use a legacy empirical approximation; AWG tables do not claim installation ampacity.

PRIVATE BY DESIGN Calculators, saved sheets and bundled references work offline. Opening manufacturer or support links requires a connection. No account, ads, tracking or subscription. Everything is included in the purchase. Your records stay on the device unless you choose to export them or use system services such as device backup.

Always check the exact manufacturer datasheet, package orientation and operating conditions before applying a reference value to hardware.

Guide updated 2026-10-31.