# DuctChecker vs THERble

The clearest difference is price: THERble at Free against DuctChecker's $6.99. THERble also leads on iOS requirement (12.0 vs 15.0). DuctChecker's advantage is update cadence (every 4 months vs every 16 months). On ads, in-app purchases and device support there is nothing between them.

THERble is free to download; DuctChecker costs $6.99 up front. Neither carries in-app purchases, so what you see is what you pay.

DuctChecker ships an update every 4 months, THERble every 16 months. The most recent releases landed on September 7, 2026 and December 12, 2025 respectively.

## The numbers

| Metric | DuctChecker | THERble |
| --- | --- | --- |
| Price | $6.99 | **Free** |
| Positive reviews | 0.0% of reviews | — |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | **Every 4 months** | Every 16 months |
| Monetization | Paid | — |
| Size | 23 MB | 46 MB |
| Requires iOS | 15.0 | **12.0** |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 17+ |
| Developer | [AIR DESIGN, INC.](https://appshunter.io/developer/923430781) | [SHIN NIPPON AIR TECHNOLOGIES CO.,LTD.](https://appshunter.io/developer/1526286874) |

## What reviewers say

### DuctChecker

[App page](https://appshunter.io/ios/app/ductchecker/id933593987)

Easily calculate duct dimensions using various engineering methods like constant pressure, static pressure regain, total pressure, and velocity. This tool simplifies complex duct design calculations, typically found in flow diagrams or slide rules.

**Highlights:** Constant pressure method calculation, Static pressure regain method, Total pressure method, Velocity method, Duct dimension determination, Simplified duct design

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### THERble

[App page](https://appshunter.io/ios/app/therble/id1630881111)

**Features:** macOS Compatibility

**In-app purchases:** none


## Frequently asked questions

### Is DuctChecker free?

DuctChecker costs $6.99, with no in-app purchases.

### Is THERble free?

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

### Do DuctChecker or THERble have ads?

Neither DuctChecker nor THERble shows ads.

### Which is updated more often, DuctChecker or THERble?

DuctChecker ships an update every 4 months, and THERble every 16 months. Most recently, DuctChecker was updated on September 7, 2026 and THERble on December 12, 2025.

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