calculation + conversion

cpc parses and evaluates strings of math, with support for units and conversion. 128-bit decimal floating points are used for high accuracy. You can mix units, like `1 km - 1m`.

Programming language: Rust
License: MIT License
Latest version: v1.2.0

cpc alternatives and similar packages

Based on the "Text processing" category

Do you think we are missing an alternative of cpc or a related project?

Add another 'Text processing' Package



calculation + conversion

cpc parses and evaluates strings of math, with support for units and conversion. 128-bit decimal floating points are used for high accuracy.

cpc lets you mix units, so for example 1 km - 1m results in Number { value: 999, unit: Meter }.

docs.rs documentation

List of all supported units

CLI Installation

To install the CLI using cargo:

cargo install cpc

To install the CLI directly, grab the appropriate binary from cpc's Releases page on GitHub, then place it wherever you normally place binaries on your OS (On Windows, you may need to edit your PATH variable or something).

CLI Usage

cpc '20c to f'

If you installed the binary somewhere that doesn't make binaries global, you would need to specify the path:

/usr/local/bin/custom/cpc '10+10'
# OR
./cpc '1" in cm'

API Installation

To install the library as a Rust dependency, add cpc to your Cargo.toml like so:

cpc = "1.*"

API Usage

use cpc::{eval};
use cpc::units::Unit;

match eval("3m + 1cm", true, Unit::Celcius, false) {
    Ok(answer) => {
        // answer: Number { value: 301, unit: Unit::Centimeter }
        println!("Evaluated value: {} {:?}", answer.value, answer.unit)
    Err(e) => {
        println!("{}", e)


3 + 4 * 2

8 % 3

(4 + 1)km to light years

10m/2s * 5 trillion s

1 lightyear * 0.001mm in km2

1m/s + 1mi/h in kilometers per h

round(sqrt(2)^4)! liters

10% of abs(sin(pi)) horsepower to watts

Supported unit types

  • Normal numbers
  • Time
  • Length
  • Area
  • Volume
  • Mass
  • Digital storage (bytes etc)
  • Energy
  • Power
  • Pressure
  • Frequency
  • Speed
  • Temperature


cpc Uses 128-bit Decimal Floating Point (d128) numbers instead of Binary Coded Decimals for better accuracy. The result cpc gives will still not always be 100% accurate. I would recommend rounding the result to 20 decimals or less.


It's pretty fast and scales well. In my case, eval() usually runs under 0.1ms. The biggest performance hit is functions like log(). log(12345) evaluates in 0.12ms, and log(e) in 0.25ms.

To see how fast it is, you can pass the --debug flag in CLI, or the debug argument to eval().


cpc returns Results with basic strings as errors. Just to be safe, you may want to handle panics (You can do that using std::panic::catch_unwind).

Dev Instructions

Get started

Install Rust. This project was built in Rust 1.45.

Run cpc with a CLI argument as input:

cargo run -- '100ms to s'

Run with debugging, which shows some extra logs:

cargo run -- '100ms to s' --debug

Run tests:

cargo test


cargo build

Adding a unit

1. Add the unit

In src/units.rs, units are specified like this:

pub enum UnitType {
  // etc

// ...

  Nanosecond:         (Time, d128!(1)),
  Microsecond:        (Time, d128!(1000)),
  // etc

The number associated with a unit is it's "weight". For example, if a second's weight is 1, then a minute's weight is 60.

I have found translatorscafe.com and calculateme.com to be good websites for unit conversion. Wikipedia is worth looking at as well.

2. Add a test for the unit

Make sure to also add a test for each unit. The tests look like this:

assert_eq!(convert_test(1000.0, Meter, Kilometer), 1.0);

Basically, 1000 Meter == 1 Kilometer.

3. Add the unit to the lexer

Text is turned into tokens (some of which are units) in lexer.rs. Here's one example:

// ...
match string {
  "h" | "hr" | "hrs" | "hour" | "hours" => tokens.push(Token::Unit(Hour)),
  // etc
// ...

Potential Improvements


  • Support for conversion between Power, Current, Resistance and Voltage. Multiplication and division is currently supported, but not conversions using sqrt or pow. #### Potential unit types Nice list of units: https://support.google.com/websearch/answer/3284611
  • Currency: How would you go about dynamically updating the weights?
  • Fuel consumption
  • Data transfer rate
  • Color codes
  • Force
  • Roman numerals
  • Angles
  • Flow rate


  1. Install Docker
  2. Install cross: cargo install cross
  3. Build for x86_64 macOS, Linux and Windows: sh cross build --release --target x86_64-apple-darwin && cross build --release --target x86_64-unknown-linux-musl && cross build --release --target x86_64-pc-windows-gnu
    • Note that building for x86_64-apple-darwin only works on macOS
    • For more targets, check out the targets cross supports
    • If you run cross build in parallel, you might get a cargo not found error The compiled binaries will now be available inside target/<target>/release/. The filename will be either cpc or cpc.exe.

Releasing a new version

  1. Update CHANGELOG.md
  2. Bump the version number in Cargo.toml and run cargo check
  3. Run cargo test
  4. Cross-compile cpc by following the steps above
  5. Commit and tag in format v0.0.0
  6. Publish on crates.io:
    1. Login by running cargo login and following the instructions
    2. Test publish to ensure there are no issues cargo publish --dry-run
    3. Publish cargo publish
  7. Publish on GitHub
    1. Zip the binaries and rename them like cpc-v1.0.0-darwin-x64
    2. Create GitHub release with release notes and attach the zipped binaries