SI Prefix Converter vs Custom Formulas
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
SI Prefix Converter
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This is a change tool of SI Prefix. It's possible to change all SI prefixes mutually.
Custom Formulas
This utility app allows users to create and manage complex calculations with multiple inputs and outputs. Formulas can be linked, grouped into categories, and customized for display precision. Share your custom calculations easily via email.
- Multiple input/output formula support
- Linked formulas via variable names
- Formula categorization
- Customizable variable display order
- Adjustable output decimal precision
- Email formula sharing
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This app is easy to use, but unlike simpler apps, multiple entered values can be fed into multiple formulas and multiple output values can be displayed. The output of one formula in a group can be fed into the next by using the same variable name. Related formulas can be grouped into categories to make them easy to find. e.g. Maths formulas, Surveying formulas, Loan interest formulas etc. The order of variables displayed to the user can be changed, as can the number of decimal digits of precision shown in the output fields. You can easily share formulas with other users of the app by emailing them. Three example formulas are pre-installed with the app. In order of increasing complexity they are: slope percentage, compound interest, and point scale factor.
Screenshots
Verdict
The clearest difference is price: SI Prefix Converter at Free against Custom Formulas's $3.99. SI Prefix Converter also leads on iOS requirement (8.0 vs 15.4). Custom Formulas's advantage is update cadence (every 5 days vs every 9 months). On ads, in-app purchases and device support there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
SI Prefix Converter is free to download; Custom Formulas costs $3.99 up front. Neither carries in-app purchases, so what you see is what you pay.
SI Prefix Converter ships an update every 9 months, Custom Formulas every 5 days. The most recent releases landed on October 13, 2026 and October 24, 2026 respectively.
| Parameter | SI Prefix Converter | Custom Formulas |
|---|---|---|
| Price | Free — better | $3.99 |
| Rating | — | 5.0 (1 ratings) — better |
| Positive reviews | — | 100.0% of reviews |
| Number of ratings | — | 1 — better |
| Update frequency | Every 9 months | Every 5 days — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | — | Paid |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Requires iOS | 8.0 — better | 15.4 |
| Further details — not scored | ||
| Size | 23 MB | 1 MB |
| Age rating | 4+ | 4+ |
| Developer | Yuki Takeda | Anthony Dunk |
In-app purchases
SI Prefix Converter
No in-app purchases
Custom Formulas
No in-app purchases
Questions
Is SI Prefix Converter free?
Is Custom Formulas free?
Do SI Prefix Converter or Custom Formulas have ads?
Which is updated more often, SI Prefix Converter or Custom Formulas?
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