Skip to content
Switch branches/tags

Ultra Fast Excel Writer for Ruby

require 'fast_excel'

workbook ="hello_world.xlsx", constant_memory: true)
  font_size: 0, # user's default
  font_family: "Arial"

worksheet = workbook.add_worksheet("Example Report")

bold = workbook.bold_format
worksheet.set_column(0, 0, FastExcel::DEF_COL_WIDTH, bold)

price = workbook.number_format("#,##0.00")
worksheet.set_column(1, 1, 20, price)

date_format = workbook.number_format("[$-409]m/d/yy h:mm AM/PM;@")
worksheet.set_column(2, 2, 20, date_format)

worksheet.append_row(["message", "price", "date"], bold)

for i in 1..1000
  worksheet.append_row(["Hello", (rand * 10_000_000).round(2),])

worksheet.append_row(["Sum","SUM(B2:B1001)")], bold)


See more examples

This repository and gem contain sources of libxlsxwriter


# Gemfile
gem 'fast_excel'


gem install fast_excel

Create Document

workbook = # creates tmp file
# ...
send_data(workbook.read_string, filename: "table.xlsx") # read tmp file and delete it

Also can use workbook.remove_tmp_file to delete tmp file manually

Constant memory mode: saves each row to disk, good for really big files but can not change previous lines that already saved

workbook = true)

Save to file

workbook ="my_dinner.xlsx")

Write Data

FastExcel will automatically detect data type and one of write_number or write_datetime or write_formula or write_string or write_url

workbook =
worksheet = workbook.add_worksheet

# write specific type value value
worksheet.write_number(row = 0, col = 5, 1_234_567, format = nil)

# write value with type detection
worksheet.write_value(row = 0, col = 5, 1_234_567, format = nil)

# write row of values. format argument can be format object or array of format objects
worksheet.write_row(row = 1, ["strong", 123_456,], format = nil)

# write row to the bottom
worksheet.append_row(["strong", 123_456,], )

# shortcut for append_row()
worksheet << ["strong", 123_456,]

Saving dates: excel store dates as number of days since 1st January 1900, and FastExcel will make it for you.

To make saving of dates slightly faster can use FastExcel.date_num helper:

date_format = workbook.number_format("[$-409]m/d/yy hh:mm;@")
worksheet.write_number(0, 0, FastExcel.date_num(,, date_format)

Formulas: special type of value in excel

worksheet << [1, 2, 3, 4]
worksheet << ["SUM(A1:D1)")] # A2 will be shown as 10

URL: Link to website or something else

url_format = workbook.add_format(underline: :underline_single, font_color: :blue) # format is optional
], url_format)
# or
worksheet.write_url(0, 2, "", url_format)

Data Formatting

format = worksheet.add_format(
  bold: true,
  italic: true,
  font_outline: true,
  font_shadow: true,
  text_wrap: true,
  font_strikeout: true,
  shrink: true,
  text_justlast: true,
  font_size: 13, # default is 11, use 0 for user's default
  font_name: "Arial", # default is Calibri, also accessible via font_family
  font_color: :orange, # can use RGB hex as "#FF0000" or 0x00FF00 or color name as symbol or string
  font_script: :font_subscript,
  rotation: 10,
  underline: :underline_single, # or :underline_double or :underline_single_accounting or :underline_double_accounting
  indent: 1,
  # border styles
  border: :border_thin,
  left: :medium,
  top: :dashed,
  right: :double,
  bottom: :hair,
  bottom_color: :alice_blue,
  top_color: "#11ABCD",
  # Align
  align: {h: :align_center, v: :align_vertical_center},
  num_format: "#,##0.00"


workbook.bold_format # bold text
workbook.number_format("[$-409]m/d/yy h:mm AM/PM;@") # format for date

Set Column Width

worksheet.set_column(start_col, end_col, width = nil, format = nil)
# or
worksheet.set_column_width(col, width = 60)
# or
worksheet.set_columns_width(start_col, end_col, width = 60)

Set Row Height

worksheet.set_row(row_num = 0, height = 30, format = nil)

Column Auto Width

Column authwidth only works for string values, because numbers may have custom formatting

Enabling column auto widths will slow down writing string values for about 15-25%

require 'fast_excel'

workbook = true)

worksheet = workbook.add_worksheet
worksheet.auto_width = true

worksheet.append_row(["some text", "some longer text for example"])

content = workbook.read_string'./some_file.xlsx', 'wb') {|f| f.write(content) }



This gem is FFI binding for libxlsxwriter C library with some syntax sugar. All original functions is avaliable, for example:

Libxlsxwriter.worksheet_activate(worksheet) # => will call void worksheet_activate(lxw_worksheet *worksheet)
# or shorter:

Full libxlsxwriter documentation:

Generated rdoc:


1000 rows:

           FastExcel:       31.7 i/s
               Axlsx:        8.0 i/s - 3.98x  slower
          write_xlsx:        6.9 i/s - 4.62x  slower

20000 rows:

           FastExcel:        1.4 i/s
               Axlsx:        0.4 i/s - 3.46x  slower
          write_xlsx:        0.1 i/s - 17.04x  slower

Max memory usage, generating 100k rows:

FastExcel   - 20 MB
Axlsx       - 60 MB
write_xlsx - 100 MB