A simple calculator is an excellent replacement for the standard application for performing calculations from an Android device.
Computations
The application is “trained” to perform four basic mathematical operations (addition, subtraction, division, multiplication), can raise numbers to powers, and also work with functions and percentages. Thanks to this program, you can easily calculate the amount of interest and the “body” of the loan, calculate the cost of fuel and even deduct taxes from sales.
Converters
A simple calculator can be used as a converter of various quantities. First of all, it supports the conversion of units of measurement - length, width, weight, volume, and so on. There is also a built-in currency converter that can automatically receive information about current courses. Well, the last “standard” converter helps determine the time in different parts of the world.
Purpose
The application got its name solely because it is as convenient and intuitive as possible. After all, it cannot be classified as a primitive calculation tool due to its rich functionality. A simple calculator will cope with a variety of tasks - from calculations for a school problem to complex accounting calculations. You can download and use it completely free. The app contains advertising but does not include paid features.
Key Features
- performing mathematical operations of varying complexity;
- conversion of currencies, time and units of measurement;
- currency exchange rate update automatic mode;
- convenient side menu providing access to all available tools;
- availability of advertising;
- saving the history of performed calculations;
- compatibility with relatively old Android versions;
- free distribution.
Calculator programs for mobile phones appeared quite a long time ago. In simple dialers, they were most often no better than individual machines, but in more advanced devices the functionality was wider. Today, when the average Android smartphone has more processing power than even the oldest computers, calculation apps have changed too. Today we will present you a selection of the best of them.
An application from Google, installed on Nexus and Pixel devices, and a standard calculator on devices with “pure” Android. 
It is a simple calculator with arithmetic and engineering functions, implemented in the standard Google Material Design style. One of the features worth noting is saving the calculation history.
Mobi Calculator
A free and fairly lightweight application for calculations with advanced functionality. In addition to the usual arithmetic expressions, in the Mobile Calculator you can set the priority of operations (for example, the result of the expression 2+2*2 - you can choose 6, or you can choose 8). It also has support for other number systems. 
Interesting features - cursor control with volume buttons (configurable separately), display of calculation results in the area below the expression window and arithmetic operations with degrees.
Calc+
Advanced computing tool. Contains a large variety of engineering functions. In addition, you can add your own constants to existing ones by clicking on the empty buttons in the engineering panel. 
Calculations of any powers, three types of logarithms and two types of roots will be especially useful for students of technical specialties. The calculation result can be easily exported.
HiPER Scientific Calculator
One of the most advanced solutions for Android. Made in the style of skeuomorphism, completely matching the appearance popular models engineering calculators. 
The number of functions is amazing - a random number generator, exponent display, support for classical and reverse Polish notation, working with fractions, and even converting the result to a Roman number. And this is far from a complete list. Disadvantages - full functionality (advanced display type) is available only in the paid version, and there is no Russian language.
CALCU
A simple but very stylish calculator with wide customization options. It performs its functions well, and simple gesture controls help with this (swipe down on the keyboard to show the search history, swipe up to switch to engineering mode). The developers have provided a variety of design themes to choose from. 
But not just themes - in the application you can customize the display of the status bar or digit separators, enable the full keyboard layout (recommended on tablets) and much more. The application is perfectly Russified. There are advertisements that can be removed by purchasing the full version.
Calculator++
Application from a Russian developer. Features an unusual approach to management - access to additional functions occurs using gestures: swiping up activates the top option, and swiping down activates the bottom one. In addition, Calculator++ has the ability to create graphs, including in 3D. 
In addition, the application supports windowed mode, running on top open source software. The only trouble is the presence of advertising, which can be removed by purchasing the paid version.
Engineering Calculator+Graphs
A solution designed for plotting graphs from MathLab. According to the developers, it is aimed at schoolchildren and students. The interface, compared to its colleagues, is quite cumbersome. 
The range of possibilities is rich. Three switchable workspaces, separate keyboards for entering alphabetic equation elements (there is also a Greek version), functions for scientific calculations. There is also a built-in library of constants and the ability to create your own function templates. The free version requires a constant connection to the Internet, and it lacks some options.
Photomath
This application is not a simple calculator. Unlike many of the calculation programs described above, Photomat does almost all the work for you - just write your task on paper and scan it. 
Then, following the application's prompts, you can calculate the result. From the outside it really looks like magic. However, Photomath also has a completely ordinary calculator, and recently it also includes handwriting. One can, perhaps, only find fault with the work of the recognition algorithms: the scanned expression is not always correctly identified.
ClevCalc
At first glance, it is a completely ordinary calculator application, without any special features. However, the development of the company ClevSoft can boast of a solid set of calculators, in the plural. 
The set of calculation templates for tasks is quite extensive - from familiar accounting calculations to average grades. This format saves a lot of time, allowing you to avoid many mistakes. Alas, such beauty has a price - the application has advertising, which it is proposed to remove by carrying out a paid upgrade to the Pro version.
WolframAlpha
Perhaps the most unusual calculator that exists. In fact, this is not a calculator at all, but a client of a powerful computing service. The application does not have the usual buttons - only a text input field in which you can enter any formulas or equations. The application will then perform the calculation and display the result. 
You can view a step-by-step explanation of the result, a visual notation, a graph or chemical formula (for physical or chemical equations), and more. Unfortunately, the program is completely paid - trial version No. Disadvantages include the lack of Russian language.
MyScript Calculator 2
Another representative of “not just calculators”, in this case focused on handwriting input. Supports basic arithmetic and algebraic expressions. 
By default, automatic calculation is enabled, but you can disable it in the settings. Recognition occurs correctly, even the worst handwriting is not a hindrance. It’s especially convenient to use this thing on devices with a stylus like the series Galaxy Note, but you can get by with your finger. The application does not have free version, so all those who liked it will have to immediately purchase it for a relatively low price.
In addition to those described above, there are dozens, or even hundreds of the most various programs for making calculations: simple, complex, there are even emulators of programmable calculators like B3-34 and MK-61, for nostalgic connoisseurs. We are sure that every user will find something suitable for themselves.
I had some difficulties using the standard calculator in Android; before that, more and more often I had to use a PC or a second phone on Symbian. Since in Android standard application did not support the root and the ability to include parentheses in expressions, and you will agree that it is not convenient to enter and memorize typical calculations in your head many times, wouldn’t it be easier to save the whole formula in a notepad and paste the formula into a calculator, and make your work more efficient and easier. We are talking about a calculator for Android “Mobi Calculator FREE”.
Functional
In fact, the calculator has all the necessary functions to consider it an engineering calculator. Here is a list of the main functions performed:
- Works with full expressions (developed based on the RPN algorithm)
- calculates interest (discounts, taxes, etc.)
- HEX/BIN/OCT mode decimal, hexadecimal, binary, octal number systems
- Timing
- Trigonometric functions. Radians and degrees with DMS mode (degree-minute-second)
- Logarithmic and other functions
- Advanced Computing History, Memory
Settings
There are four items in the engineering calculator settings:
- Display - theme (skin) settings are collected here, appearance, number displays (fraction separator, digit group separator)
- Controls - this section contains button sound settings, gesture control settings, and other key settings
- Calculation - here are the settings for calculation accuracy, rounding, calculation methods
- Storage - this section contains history settings - storage duration, number of stored records, actions with history
It will be very convenient to have a history in which you can place any important calculations.
Bottom line
The calculator is much more functional than the standard one, and it is free.