Simple Calculator

Simple Calculator is an open-source scientific calculator and unit converter in one small Android app. Its calculation engine uses Java BigDecimal rather than binary double values, and its unit definitions are bundled with the app instead of fetched from a service.

This is the newer project by Hobby Projects Lab, first added to F-Droid in October 2026. It is not the former Simple Mobile Tools app with the same name, or that app’s Fossify Calculator successor.

This page covers F-Droid’s 1.0.2 source build. We matched the 2.2 MB APK to F-Droid’s signed index, inspected its single manifest permission and read the exact v1.0.2 source used by the recipe. We did not compare its results against laboratory or financial software, so it should not be treated as a certified measurement tool.

Scientific calculations and precision

The normal keypad handles arithmetic, powers, square and general roots, percentages, modulus and factorials. The function panels add base-10 and arbitrary-base logarithms, natural logs, trigonometric and inverse functions, hyperbolic functions, absolute value, π and e. A switch changes trigonometry between radians and degrees.

Settings allow 0 to 100 decimal places, rounded half-up. For each result, the source recalculates with progressively higher internal precision until the displayed rounding stabilises or its own limit is reached. That is more deliberate than formatting a hardware floating-point answer, but it is not unlimited: the engine rejects values outside roughly ±10¹⁰⁰ and factorial input above 69.

Expressions show a live preview as you type. Pressing equals adds the expression to a tappable history so it can be restored and edited. That list lives in the calculator ViewModel rather than a database: it survives ordinary screen recomposition, but it is not a permanent calculation archive and is cleared with the app process or the clear-all action.

Sixteen offline conversion categories

The converter updates while you type and covers length, time, speed, mass, area, volume, density, temperature, force, energy, work, power, pressure, angle, frequency and digital storage. This includes metric and imperial units as well as decimal and binary storage sizes.

Conversions use the same configurable decimal precision as calculations. Version 1.0.2 fixes the swap control and rejects temperatures below absolute zero instead of presenting a physically impossible converted value. Rates that change over time, such as currencies or cryptocurrency prices, are deliberately absent because the app contains no online data source.

Offline privacy and local state

The measured manifest contains only Android’s automatically generated DYNAMIC_RECEIVER_NOT_EXPORTED_PERMISSION; there is no internet permission, advertising SDK or tracker found by our scan. Calculation history is kept in memory, while the precision preference uses Android DataStore. The manifest permits Android system backup and its backup-rule files are empty templates, so that stored preference may be included in a device backup.

About this file

• This is 1.0.2 (version code 2), indexed by F-Droid and signed with the developer certificate recorded there. The developer’s GitHub release uses the same signer and can update this installation in place.
• The 2,227,036-byte APK needs Android 7.0 or later and includes 32- and 64-bit ARM and x86 native libraries.
• Its measured SHA-256 is 2bc08df01ac6fb3ff482db03fd0db79dd868924d4456e8774b3f4929186a67d1, matching F-Droid’s signed index.
• It declares one generated internal permission, has no internet permission and our scan found no known tracker SDKs.
• Simple Calculator is licensed under GPL-3.0-or-later. The bundled Quicksand font is under the SIL Open Font License 1.1.

CPU types in this build: arm64-v8a (64-bit ARM, almost every phone since 2017); armeabi-v7a (32-bit ARM, older and budget phones); x86 (32-bit Intel, emulators); x86_64 (64-bit Intel, emulators and Chromebooks).