---
title: "Handling money in ruby"
description:
  "Float in ruby is not good for calculations. That makes it difficult to use
  float for money in a ruby based application. See this blog for a solution."
canonical_url: "https://www.bigbinary.com/blog/handling-money-in-ruby"
markdown_url: "https://www.bigbinary.com/blog/handling-money-in-ruby.md"
---

# Handling money in ruby

Float in ruby is not good for calculations. That makes it difficult to use float
for money in a ruby based application. See this blog for a solution.

- Author: Neeraj Singh
- Published: January 14, 2013
- Categories: Ruby

In ruby do not use float for calculation since float is not good for precise
calculation.

```ruby
irb(main):001:0> 200 * (7.0/100)
=> 14.000000000000002
```

7 % of 200 should be 14. But float is returning `14.000000000000002` .

In order to ensure that calculation is right make sure that all the actors
participating in calculation is of class
[BigDecimal](http://www.ruby-doc.org/stdlib-1.9.3/libdoc/bigdecimal/rdoc/BigDecimal.html)
. Here is how same operation can be performed using BigDecimal .

```ruby
irb(main):003:0> result = BigDecimal.new(200) * ( BigDecimal.new(7)/BigDecimal.new(100))
=> #<BigDecimal:7fa5eefa1720,'0.14E2',9(36)>
irb(main):004:0> result.to_s
=> "14.0"
```

As we can see BigDecimal brings much more accurate result.

## Converting money to cents

In order to charge the credit card using [Stripe](https://stripe.com/) we needed
to have the amount to be charged in cents. One way to convert the value in cents
would be

```ruby
amount  = BigDecimal.new(200) * ( BigDecimal.new(7)/BigDecimal.new(100))
puts (amount * 100).to_i #=> 1400
```

Above method works but I like to delegate the functionality of making money out
of a complex BigDecimal value to gem like
[money](https://rubygems.org/gems/money) . In this project we are using
[activemerchant](https://rubygems.org/gems/activemerchant) which depends on
money gem . So we get money gem for free. You might have to add money gem to
Gemfile if you want to use following technique.

money gem lets you get a money instance out of BigDecimal.

```ruby
amount  = BigDecimal.new(200) * ( BigDecimal.new(7)/BigDecimal.new(100))
amount_in_money = amount.to_money
puts amount_in_money.cents #=> 1400
```

## Stay in BigDecimal or money mode for calculation

If you are doing any sort of calculation then all participating elements must be
either BigDecimal or Money instance. It is best if all the elements are of the
same type.

## Links

- [Human page](https://www.bigbinary.com/blog/handling-money-in-ruby)