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Category Text Formatting

Number or String Enter the value you want to pad

Pad Character Single character

Target Width Total characters (max 1000)

Pad Direction

Presets:

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About

String padding errors cause silent data corruption in databases, CSV exports, and API payloads. A ZIP code of 7310 instead of 07310 routes mail to the wrong state. An invoice number missing its leading zeros breaks sort order across accounting systems. This tool applies deterministic character padding to any numeric string, letting you specify the fill character c, target width w, and alignment direction. It handles edge cases that naive implementations miss: inputs already exceeding target width are returned unchanged, and center-padding distributes the remainder with floor on the left and ceil on the right to maintain visual balance.

The tool preserves sign characters and decimal points as part of the input string. It does not interpret numeric value. This is intentional. Padding operates on the string representation, not the number. If you need to pad -42 to width 6 with zeros, the result is 00-42, not -00042. For sign-aware padding, pre-process by separating the sign before padding the magnitude.

Formulas

Padding computes the number of fill characters needed as the difference between the target width and the current string length, clamped to zero.

padding = max(0, w − len(s))

For left-padding, all padding characters are prepended. For right-padding, all are appended. For center-padding, the distribution is:

left = floor(padding2)

right = ceil(padding2)

Where w is the desired total width, s is the input string, c is the pad character (single character), and len returns the string length. When len(s) ≥ w, the original string is returned unmodified.

Reference Data

Use Case	Input	Pad Char	Width	Direction	Result
US ZIP Code	7310	0	5	Left	07310
Invoice Number	42	0	8	Left	00000042
Binary Byte	101	0	8	Left	00000101
Hex Color Code	FF	0	6	Left	0000FF
Fixed-Width Column	99	Space	10	Right	99········
Centered Label	42	-	10	Center	----42----
Centered Odd Remainder	7	*	6	Center	7*
SSN Fragment	56	0	4	Left	0056
Already Full Width	12345	0	3	Left	12345
Decimal Price	9.5	0	6	Left	0009.5
Batch ID	3	0	12	Left	000000000003
Table Separator	100	.	8	Right	100.....
Empty Input	(empty)	0	4	Left	0000
Single Digit Year	5	0	2	Left	05
Product SKU	891	0	10	Left	0000000891

Frequently Asked Questions

This tool performs string-level padding, not numeric-aware formatting. The minus sign is treated as an ordinary character within the string. If you need sign-aware zero-padding, strip the sign before padding, then re-prepend it. For example, separate "-" and "42", pad "42" to width 5 producing "00042", then concatenate to get "-00042".

The input is returned unchanged. The padding count formula is max(0, w − len(s)). When len(s) ≥ w, the result is 0 fill characters. No truncation occurs. This is consistent with the behavior of padStart() and padEnd() in ECMAScript 2017+.

When the padding count is odd, the extra character goes to the right side. Specifically, the left side receives floor(padding / 2) characters and the right side receives ceil(padding / 2). For example, padding "7" to width 6 with "*" produces "**7***" - 2 on the left, 3 on the right.

No. The pad character field is restricted to a single character. Multi-character padding patterns introduce ambiguity when the remaining space is not evenly divisible by the pattern length. If you need repeating patterns, pad with a single character first, then find-and-replace in a text editor.

Yes. The target width is capped at 1000 characters. Creating strings beyond this length in a browser environment is technically possible, but serves no practical formatting purpose and risks UI rendering delays. Most real-world padding use cases (ZIP codes, invoice numbers, binary bytes) require widths under 64.

It works with any single Unicode character that JavaScript's String.length counts as 1. Most emoji are represented as surrogate pairs (length 2), so they will be rejected by the single-character validation. Standard accented characters (é, ñ, ü) work correctly as they are single code units in UTF-16.