vec_fmt_number_si: Format a vector as numbers with SI prefixes

In gt: Easily Create Presentation-Ready Display Tables

Format a vector as numbers with SI prefixes

Description

With numeric values in a vector, we can format the values with SI (International System of Units) prefixes. These prefixes like k (kilo), M (mega), G (giga), and m (milli) scale numbers in either powers of 1000 (engineering mode) or powers of 10 and 100 (decimal mode).

We have control over the formatting with the following options:

• decimals: choice of the number of decimal places, option to drop trailing zeros, and a choice of the decimal symbol

• scaling: we can choose to scale targeted values by a multiplier value (useful for unit conversions)

• SI prefix mode: choose between engineering prefixes (powers of 1000) or decimal prefixes (all SI prefixes)

• units: an optional unit designation for the values

• pattern: option to use a text pattern for decoration of the formatted values

• locale-based formatting: providing a locale ID will result in formatting specific to the chosen locale

Usage

vec_fmt_number_si(
  x,
  unit = NULL,
  decimals = 2,
  drop_trailing_zeros = FALSE,
  drop_trailing_dec_mark = TRUE,
  scale_by = 1,
  prefix_mode = c("engineering", "decimal"),
  pattern = "{x}",
  sep_mark = ",",
  dec_mark = ".",
  force_sign = FALSE,
  incl_space = TRUE,
  locale = NULL,
  output = c("auto", "plain", "html", "latex", "rtf", "word")
)

Arguments

x	The input vector vector(numeric|integer) // required This is the input vector that will undergo transformation to a character vector of the same length. Values within the vector will be formatted.
unit	Unit to append to formatted values ⁠scalar<character>⁠ // default: NULL (optional) A character string specifying the unit to append after the SI prefix (e.g., "g" for grams, "W" for watts, "Hz" for hertz, "m" for meters). If NULL, only the prefix will be shown. The unit can also be dynamically specified per row using from_column().
decimals	Number of decimal places scalar<numeric|integer>(val>=0) // default: 2 The exact number of decimal places to display in the mantissa. If both decimals and n_sigfig are provided, n_sigfig takes precedence.
drop_trailing_zeros	Drop trailing zeros ⁠scalar<logical>⁠ // default: FALSE Remove trailing zeros after the decimal point (e.g., "1.50" becomes "1.5").
drop_trailing_dec_mark	Drop trailing decimal mark ⁠scalar<logical>⁠ // default: TRUE Remove the decimal mark if all decimal places are zero (e.g., "1." becomes "1").
scale_by	Scale values by a fixed multiplier ⁠scalar<numeric|integer>⁠ // default: 1 All numeric values will be multiplied by the scale_by value before undergoing formatting. Since the default value is 1, no values will be changed unless a different multiplier value is supplied. This is useful for unit conversions, such as using unit_conversion() to convert horsepower to watts before formatting with SI prefixes.
prefix_mode	Type of SI prefixes to use ⁠singl-kw:[engineering|decimal]⁠ // default: "engineering" The type of SI prefixes to use. Options are "engineering" (powers of 1000 only) or "decimal" (all SI prefixes including powers of 10 and 100). See the SI Prefix Modes section for details.
pattern	Decoration pattern ⁠scalar<character>⁠ // default: "{x}" A formatting pattern for decorating values. Use {x} to represent the formatted value (including prefix and unit).
sep_mark	Thousands separator ⁠scalar<character>⁠ // default: "," The character to use as the thousands separator. Overridden if locale is provided.
dec_mark	Decimal mark ⁠scalar<character>⁠ // default: "." The character to use as the decimal point. Overridden if locale is provided.
force_sign	Force positive sign ⁠scalar<logical>⁠ // default: FALSE Force the display of a plus sign for positive values.
incl_space	Include a space between the value and the unit symbol ⁠scalar<logical>⁠ // default: TRUE An option for whether to include a space between the numerical value and the SI prefix + unit (e.g., TRUE for "1.5 kW", FALSE for "1.5kW"). Per SI convention, there should be a space between the value and the unit symbol.
locale	Locale identifier ⁠scalar<character>⁠ // default: NULL (optional) An optional locale identifier that can be used for formatting values according to the locale's rules. Examples include "en" for English (United States) and "fr" for French (France). We can call info_locales() for a useful reference for all of the locales that are supported.
output	Output format ⁠singl-kw:[auto|plain|html|latex|rtf|word]⁠ // default: "auto" The output style of the resulting character vector. This can either be "auto" (the default), "plain", "html", "latex", "rtf", or "word". In knitr rendering (i.e., Quarto or R Markdown), the "auto" option will choose the correct output value

Value

A character vector.

Examples

Let's create a numeric vector for the next few examples:

num_vals <- c(1.5e9, 2.7e6, 4200, 0.3, 0.00012, 2.4e-8)

Using vec_fmt_number_si() with the default options will create a character vector with values formatted with SI prefixes. Any NA values remain as NA values. The rendering context will be autodetected unless specified in the output argument (here, it is of the "plain" output type).

vec_fmt_number_si(num_vals)

#> [1] "1.50 G" "2.70 M" "4.20 k" "300.00 m" "120.00 u" "24.00 n"

We can add a unit designation to all values with the unit option:

vec_fmt_number_si(num_vals, unit = "W")

#> [1] "1.50 GW" "2.70 MW" "4.20 kW" "300.00 mW" "120.00 uW" "24.00 nW"

We can change the number of decimal places with the decimals option:

vec_fmt_number_si(num_vals, unit = "g", decimals = 0)

#> [1] "2 Gg" "3 Mg" "4 kg" "0 g" "0 g" "0 g"

If we are formatting for a different locale, we could supply the locale ID and gt will handle any locale-specific formatting options:

vec_fmt_number_si(num_vals, unit = "m", locale = "fr")

#> [1] "1,50 Gm" "2,70 Mm" "4,20 km" "300,00 mm" "120,00 um" "24,00 nm"

The scale_by option is useful for unit conversions. For instance, to convert meters to millimeters:

vec_fmt_number_si(c(0.5, 1.2, 3.8), unit = "m", scale_by = 1000)

#> [1] "500.00 mm" "1.20 km" "3.80 km"

We can control the space between the number and unit with incl_space:

vec_fmt_number_si(num_vals, unit = "Hz", incl_space = FALSE, decimals = 1)

#> [1] "1.5GHz" "2.7MHz" "4.2kHz" "300.0mHz" "120.0uHz" "24.0nHz"

As a last example, one can wrap the values in a pattern with the pattern argument. Note here that NA values won't have the pattern applied.

vec_fmt_number_si(num_vals, pattern = "[{x}]")

#> [1] "[1.50 G]" "[2.70 M]" "[4.20 k]" "[300.00 m]" "[120.00 u]" "[24.00 n]"

Function ID

15-5

Function Introduced

v1.2.0 (December 16, 2025)

See Also

The variant function intended for formatting gt table data: fmt_number_si().

Other vector formatting functions: vec_fmt_bytes(), vec_fmt_currency(), vec_fmt_date(), vec_fmt_datetime(), vec_fmt_duration(), vec_fmt_engineering(), vec_fmt_fraction(), vec_fmt_index(), vec_fmt_integer(), vec_fmt_markdown(), vec_fmt_number(), vec_fmt_partsper(), vec_fmt_percent(), vec_fmt_roman(), vec_fmt_scientific(), vec_fmt_spelled_num(), vec_fmt_time()

gt documentation built on Jan. 22, 2026, 9:07 a.m.