# Resistor Tools vs 555 Calc

The clearest difference is rating: Resistor Tools at 5.0 against 555 Calc's 4.0. Resistor Tools also leads on ads (none vs shown) and update cadence (every 2 months vs every 20 months). 555 Calc's advantage is in-app purchases (none vs 1). On price, device support and iOS requirement there is nothing between them.

Both are free to download. Resistor Tools sells 1 one-off in-app purchase. 555 Calc asks for nothing beyond the download.

Resistor Tools holds the better App Store score, 5.0 against 4.0. Both are backed by a comparable volume of ratings — 10 and 3 respectively. Written reviews point the same way: 75% of Resistor Tools's written reviews are positive against 50% of 555 Calc's.

Resistor Tools ships an update every 2 months, 555 Calc every 20 months. The most recent releases landed on October 10, 2026 and September 27, 2026 respectively.

## The numbers

| Metric | Resistor Tools | 555 Calc |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[5.0 (10 ratings)](https://appshunter.io/ios/app/resistor-tools/id826045228/reviews)** | [4.0 (3 ratings)](https://appshunter.io/ios/app/555-calc/id868058244/reviews) |
| Number of ratings | **10** | 3 |
| Positive reviews | **75.0% of reviews** | 50.0% of reviews |
| In-app purchases | Yes | **No** |
| Ads | **No** | Yes |
| Update frequency | **Every 2 months** | Every 20 months |
| Monetization | Free with in-app purchases | **Ad-supported** |
| Size | 4 MB | 18 MB |
| Requires iOS | 12.0 | **11.0** |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 4+ |
| Developer | [Siu Yuen Ho](https://appshunter.io/developer/814088527) | [Jibiki Works](https://appshunter.io/developer/556845808) |

## What reviewers say

### Resistor Tools

[App page](https://appshunter.io/ios/app/resistor-tools/id826045228)

This utility app provides a suite of tools for calculating and determining resistor values. It assists hobbyists and engineers with series, parallel, and voltage divider calculations, as well as inverting amplifier gain.

**Highlights:** Series and parallel resistor calculation, Resistor combination finder, Voltage divider ratio and value calculation, Inverting amplifier gain calculation, Save combinations to CSV

**Features:** Vision Pro support

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Unlock pro feature | $0.99 | one-time |


### 555 Calc

[App page](https://appshunter.io/ios/app/555-calc/id868058244)

This utility app helps engineers and hobbyists calculate resistor values for circuits using the Timer IC 555. Simply input frequency, duty ratio, and capacitor values to get the required resistor outputs.

**Highlights:** Calculate resistor values, Input frequency, Input duty ratio, Input capacitor value, Timer IC 555 circuit design

**Features:** macOS Compatibility

**In-app purchases:** none


## Frequently asked questions

### Is Resistor Tools free?

Resistor Tools is free to download, with in-app purchases available.

### Is 555 Calc free?

555 Calc is free to download, with no in-app purchases.

### Which has better reviews, Resistor Tools or 555 Calc?

Resistor Tools is rated higher. Resistor Tools averages 5.0 out of 5 from 10 ratings, while 555 Calc averages 4.0 from 3 ratings.

### Do Resistor Tools or 555 Calc have ads?

555 Calc shows ads; Resistor Tools does not.

### Which is updated more often, Resistor Tools or 555 Calc?

Resistor Tools ships an update every 2 months, and 555 Calc every 20 months. Most recently, Resistor Tools was updated on October 10, 2026 and 555 Calc on September 27, 2026.

---

*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*