diff --git a/lib/crutches/format/number.ex b/lib/crutches/format/number.ex
index 8d06aa5..c4ed40c 100644
--- a/lib/crutches/format/number.ex
+++ b/lib/crutches/format/number.ex
@@ -418,4 +418,260 @@ defmodule Crutches.Format.Number do
   def as_percentage!(number, opts) do
     as_percentage(number, opts)
   end
+
+  @doc ~S"""
+  Formats and approximates `number` for human readability.
+
+  `1200000000` becomes `"1.2 Billion"`. This is useful as larger numbers become
+  harder to read.
+
+  See `as_human_size` if you want to print a file size.
+
+  You can also define you own unit-quantifier names if you want to use other
+  decimal units (eg.: 1500 becomes "1.5 kilometers", 0.150 becomes
+  “150 milliliters”, etc). You may define a wide range of unit quantifiers, even
+  fractional ones (centi, deci, mili, etc).
+
+  # Options
+
+  - `:locale` (atom) --- Locale to be used for formatting. *Default:*
+  current locale.
+  - `:precision` (integer) --- Precision of the number. *Default:* `3`
+  - `:significant` - If true, precision will be the # of significant_digits. If
+  false, the # of fractional digits (defaults to true)
+  - `:separator` (string) --- Separator between the fractional and integer
+  digits. *Default:* `"."`
+  - `:delimiter` (string) --- Thousands delimiter. *Default:* `""`
+  -`:units` (keyword list/string) --- Keyword list of unit quantifier names,
+  *or* a string containing an i18n scope pointing to it.
+  - `:format` (string) --- Format of the output string. `%u` is the quantifier,
+  `%n` is the number. *Default:* `"%n %u"`
+
+  # i18n
+
+  This function takes a keyword list of quantifier names to use for formatting.
+  It supports the following keys:
+
+  - `:unit`
+  - `:ten`
+  - `:hundred`
+  - `:thousand`
+  - `:million`
+  - `:billion`
+  - `:trillion`
+  - `:quadrillion`
+  - `:deci`
+  - `:centi`
+  - `:milli`
+  - `:micro`
+  - `:nano`
+  - `:pico`
+  - `:femto`
+
+  # Examples
+
+      iex> Number.as_human(123)
+      "123"
+
+      iex> Number.as_human(1234)
+      "1.23 Thousand"
+
+      iex> Number.as_human(12345)
+      "12.3 Thousand"
+
+      iex> Number.as_human(1234567)
+      "1.23 Million"
+
+      iex> Number.as_human(1234567890)
+      "1.23 Billion"
+
+      iex> Number.as_human(1234567890123)
+      "1.23 Trillion"
+
+      iex> Number.as_human(1234567890123456)
+      "1.23 Quadrillion"
+
+      iex> Number.as_human(1234567890123456789)
+      "1230 Quadrillion"
+
+      iex> Number.as_human(489939, precision: 2)
+      "490 Thousand"
+
+      iex> Number.as_human(489939, precision: 4)
+      "489.9 Thousand"
+
+      iex> Number.as_human(1234567, precision: 4, significant: false)
+      "1.2346 Million"
+
+      iex> Number.as_human(1234567, precision: 1, separator: ",", significant: false)
+      "1,2 Million"
+
+      iex> Number.as_human(500000000, precision: 5)
+      "500 Million"
+
+      iex> Number.as_human(12345012345, significant: false)
+      "12.345 Billion"
+
+      iex> Number.as_human!("abc")
+      ** (ArithmeticError) bad argument in arithmetic expression
+  """
+  @as_human [
+    valid: [:locale, :precision, :significant, :separator, :delimiter,
+      :strip_insignificant_zeros, :units, :format],
+    defaults: [
+      precision: 3,
+      significant: true,
+      separator: ".",
+      delimiter: "",
+      strip_insignificant_zeros: true,
+      units: [
+        quadrillion: "Quadrillion",
+        trillion: "Trillion",
+        billion: "Billion",
+        million: "Million",
+        thousand: "Thousand",
+        hundred: "",
+        ten: "",
+        unit: "",
+        deci: "deci",
+        centi: "centi",
+        milli: "milli",
+        micro: "micro",
+        nano: "nano",
+        pico: "pico",
+        femto: "femto"
+      ],
+      format: "%n %u"
+    ]
+  ]
+
+  def as_human(number, opts \\ [])
+  def as_human(number, opts) when is_number(number) do
+    opts = Option.combine!(opts, @as_human)
+    {exp, unit, sign} = closest_size_and_sign(number)
+
+    precision = opts[:precision]
+
+    if precision < 0 do
+      precision = 0
+    end
+
+    delimited_opts = Keyword.take(opts, @as_delimited[:valid])
+
+    fract_num =
+      abs(number) / :math.pow(10, exp)
+      |> rounded_or_significant(opts[:significant], precision)
+      |> strip_trailing_zeros(opts[:strip_insignificant_zeros])
+      |> as_delimited(delimited_opts)
+
+    if sign < 0 do
+      fract_num = "-" <> fract_num
+    end
+
+    format_as_human(fract_num, opts[:units][unit], opts[:format])
+  end
+
+  defp closest_size_and_sign(number) when is_number(number) do
+    tenth_exp =
+      number
+      |> abs
+      |> :math.log10
+      |> trunc
+
+    sign = number_sign(number)
+
+    cond do
+      tenth_exp >= 15 -> {15, :quadrillion, sign}
+      tenth_exp >= 12 -> {12, :trillion, sign}
+      tenth_exp >= 9  -> {9, :billion, sign}
+      tenth_exp >= 6  -> {6, :million, sign}
+      tenth_exp >= 3  -> {3, :thousand, sign}
+      tenth_exp >= 2  -> {0, :hundred, sign}
+      tenth_exp >= 1  -> {0, :ten, sign}
+      tenth_exp >= 0  -> {0, :unit, sign}
+      tenth_exp < 0  && tenth_exp >= -1  -> {-1, :deci, sign}
+      tenth_exp < -1 && tenth_exp >= -2  -> {-2, :centi, sign}
+      tenth_exp < -2 && tenth_exp >= -3  -> {-3, :milli, sign}
+      tenth_exp < -3 && tenth_exp >= -6  -> {-6, :micro, sign}
+      tenth_exp < -6 && tenth_exp >= -9  -> {-9, :nano, sign}
+      tenth_exp < -9 && tenth_exp >= -12 -> {-12, :pico, sign}
+      tenth_exp < -12 -> {-15, :femto, sign}
+    end
+  end
+
+  defp number_sign(number) when is_number(number) do
+    cond do
+      number >= 0 ->  1
+      true -> -1
+    end
+  end
+
+  defp rounded_or_significant(number, significant, precision) do
+    case significant do
+      true ->
+        make_significant(number, precision)
+      false ->
+        number = Float.round(number, precision)
+
+        if precision > 0 do
+          :io_lib.format("~.#{precision}f", [number]) |> List.to_string
+        else
+          number |> trunc |> Integer.to_string
+        end
+    end
+  end
+
+  defp make_significant(number, precision) do
+    digits = (:math.log10(number) + 1) |> Float.floor |> trunc
+    multiplier = :math.pow(10, digits - precision)
+    extra_precision = precision - digits
+
+    result = Float.round(number / multiplier) * multiplier
+
+    if extra_precision > 0 do
+      :io_lib.format("~.#{extra_precision}f", [result]) |> List.to_string
+    else
+      result |> trunc |> Integer.to_string
+    end
+  end
+
+  defp strip_trailing_zeros(number, strip) do
+    if strip do
+      strip_trailing_zeros(number)
+    else
+      number
+    end
+  end
+
+  defp strip_trailing_zeros(number) do
+    if String.contains?(number, ".") do
+      case String.reverse(number) do
+        "0" <> number -> String.reverse(number) |> strip_trailing_zeros
+        "." <> number -> String.reverse(number)
+        number -> String.reverse(number)
+      end
+    else
+      number
+    end
+  end
+
+  defp format_as_human(binary, unit, format) when is_binary(binary) do
+    str = String.replace(format, "%n", binary, global: false)
+    String.replace(str, "%u", unit, global: false) |> String.strip
+  end
+
+  @doc ~S"""
+  Throwing version of `as_human`, raises if the input is not a valid number.
+  """
+  def as_human!(number, opts \\ [])
+  def as_human!(number, opts) when is_binary(number) do
+    case Float.parse(number) do
+      {num, ""} -> as_human(num, opts)
+              _ -> raise(ArithmeticError, message: "bad argument in arithmetic expression")
+    end
+  end
+
+  def as_human!(number, opts) when is_number(number) do
+    as_human(number, opts)
+  end
 end