Numeral

Lightweight number formatting and parsing for Dart.

Numeral focuses on the display formats that application code reaches for every day: decimals, compact numbers, percentages, byte sizes, and simple currency strings. Create a codec once, keep it in your app utilities, and use it for both formatting and parsing.

Installation

Add Numeral to your pubspec.yaml:

dependencies:
  numeral: ^4.0.0

Usage

Import the codec entrypoint for built-in number display codecs:

import 'package:numeral/codec.dart';
import 'package:numeral/en.dart' as en;

package:numeral/numeral.dart contains the core protocols and shared models: NumeralCodec, NumeralLanguage, NumeralUnitSet, NumeralUnit, and Rounding.

Create reusable codec instances:

final fileSize = BytesCodec.binary(maxFractionDigits: 1);
final compact = en.compact(maxFractionDigits: 1);
final ratio = PercentCodec(maxFractionDigits: 2);

fileSize.format(1536); // 1.5 KiB
fileSize.parse('1.5 KiB'); // 1536
fileSize.encode(1536); // 1.5 KiB
fileSize.decode('1.5 KiB'); // 1536

compact.format(12345); // 12.3K
compact.parse('12.3K'); // 12300

ratio.format(0.1234); // 12.34%
ratio.parse('12.34%'); // 0.1234

For one-off formatting, import the extension entry:

import 'package:numeral/extension.dart';
import 'package:numeral/zh.dart' as zh;

12345.compact(maxFractionDigits: 1); // 12.3K
1536.bytes(binary: true, maxFractionDigits: 1); // 1.5 KiB
1000000.currency('¥', style: zh.compact(maxFractionDigits: 0)); // ¥100万
1000000.formatWith(zh.cardinal()); // 一百万

Codecs

Each codec extends Codec<T, String> from dart:convert.

format and parse are readable aliases for encode and decode, so both styles work:

final bytes = BytesCodec.binary();

bytes.format(1024); // 1 KiB
bytes.encode(1024); // 1 KiB
bytes.parse('1 KiB'); // 1024
bytes.decode('1 KiB'); // 1024

Unit-style codecs such as compact numbers, percentages, byte sizes, and currency can replace their internal number style with another codec. By default, they use a DecimalCodec built from their decimal options.

Decimal

final amount = DecimalCodec(
  minFractionDigits: 2,
  maxFractionDigits: 2,
);

amount.format(1234567.8); // 1,234,567.80
amount.parse('1,234,567.80'); // 1234567.8

Compact

import 'package:numeral/en.dart' as en;

final compact = en.compact(maxFractionDigits: 1);

compact.format(1234); // 1.2K
compact.format(999999); // 1M
compact.parse('3 million'); // 3000000

Custom unit sets use the same NumeralUnit model as byte codecs:

import 'package:numeral/codec.dart';
import 'package:numeral/numeral.dart';

final custom = CompactCodec(
  unitSet: NumeralUnitSet([
    NumeralUnit(1, ''),
    NumeralUnit(1000, 'K', aliases: ['k']),
    NumeralUnit(1000000, 'M', aliases: ['m']),
  ]),
);

custom.format(1234567); // 1.23M
custom.parse('3.5M'); // 3500000

Custom unit scales must be finite, positive, and strictly ascending. Parser tokens are matched case-insensitively, so symbols and aliases should be unique after lowercasing.

Percent

final percent = PercentCodec(maxFractionDigits: 1);

percent.format(0.1234); // 12.3%
percent.parse('12.3%'); // 0.123

Bytes

final decimalBytes = BytesCodec();
final binaryBytes = BytesCodec.binary(maxFractionDigits: 1);

decimalBytes.format(1500); // 1.5 KB
decimalBytes.parse('1.5 MB'); // 1500000

binaryBytes.format(1536); // 1.5 KiB
binaryBytes.parse('1.5 KiB'); // 1536

Currency

Currency formatting is display-oriented. Use a decimal or money type for financial calculation, then use Numeral to render and parse strings.

import 'package:numeral/zh.dart' as zh;

final usd = CurrencyCodec(r'$');
final cny = CurrencyCodec(
  '¥',
  style: zh.compact(maxFractionDigits: 0),
);

usd.format(1234.5); // $1,234.50
usd.parse(r'$1,234.50'); // 1234.5
cny.format(1000000); // ¥100万
cny.parse('¥100万'); // 1000000

Parsing

Every codec has parse and tryParse:

final bytes = BytesCodec.binary();

bytes.parse('1 KiB'); // 1024
bytes.tryParse('bad input'); // null

parse returns the natural numeric type for the codec:

• DecimalCodec.parse(...) returns num.
• CompactCodec.parse(...) returns num.
• PercentCodec.parse(...) returns double.
• BytesCodec.parse(...) returns int.
• CurrencyCodec.parse(...) returns num.

Language Paths

Built-in language packs live behind separate import paths. This keeps the core API small while allowing locale-specific rules to include code, not only unit data.

import 'package:numeral/zh.dart' as zh;

final compact = zh.compact(maxFractionDigits: 2);
final words = zh.cardinal();
final year = zh.year();
final financial = zh.financial();
final rmb = zh.rmb();

compact.format(1234567); // 123.46万
words.format(1000000); // 一百万
words.format(2000000); // 二百万
words.parse('一百万'); // 1000000
words.parse('两百万'); // 2000000
words.parse('一万零十'); // 10010
words.parse('一万二'); // 12000
year.format(2026); // 二〇二六
financial.format(1000000); // 壹佰万
rmb.format(1000000); // 人民币壹佰万元整
rmb.format(1234567.89); // 人民币壹佰贰拾叁万肆仟伍佰陆拾柒元捌角玖分

External packages can build the same style of language path by reusing NumeralLanguage, NumeralUnitSet, and NumeralCodec.

License

This library is licensed under the MIT License.