Replace '#'

Writers often use the hash sign (#) as shorthand for "number," "No.," or an ordinal. That works in technical or UI contexts but often reads informal, ambiguous, or ungrammatical in prose. Below are clear rules, many ready-to-use rewrites, and quick tests to fix sentences fast.

Quick answer

Keep # only when the audience expects a symbol (hashtags, code, issue trackers). In prose, use No. for labels, the word number or a numeral for counts, and ordinals for ranks.

Label/ID: use No. - e.g., Case No. 7, Issue No. 42.
Count in running text: write the numeral (500) or spell it out per your style guide.
Rank/sequence: use an ordinal - e.g., she finished first, not she finished #1 in narrative prose.

Core explanation: what # means and why to change it

The hash is a symbol that labels or tags; it doesn't function as a grammatical word. Replacing # with No., number, or an ordinal restores clarity and fits sentence structure.

Keep the symbol where readers expect tokens: spreadsheets, issue trackers, or social tags. For reader-facing prose, prefer words or standard abbreviations and be consistent across a document.

# is fine for tags, IDs, short UI labels, and developer contexts.
In running text, replace # with No. (label), number (noun), or an ordinal (rank).
Don't mix forms without reason - avoid #1 in one paragraph and "number one" in the next.

When the hash sign is acceptable (real usage)

Keep # where the audience expects a symbol: social hashtags, code, logs, internal ticket references, and compact UI labels. Avoid it in narrative sentences aimed at a broad audience.

Social tags: #BlackFriday stays as a tag.
Developer/issue trackers: bug #451 internally; public report: Bug No. 451.
Spreadsheet headers or inventory labels: SKU #300 is fine in a table; write "SKU number 300" in narrative.

Example: Hashtag: use #ThrowbackThursday on social media.
Work: Internal bug note: refer to bug #342. External update: Bug No. 342 has been fixed.

Grammar rules: choosing No., number, or an ordinal

Decide whether the number is an ID/label, a noun (count), or a rank. Use No. for labels, numerals or spelled-out words for counts, and ordinals for ranks or positions.

No. is an abbreviation-include the period (No.) in most styles. Ordinals (first, second) read naturally for positions.

Label: No. 5, Case No. 7, Client No. 2.
Count: 500 attendees, 1,000 followers (use commas per your style guide).
Rank/sequence: She finished first; use ordinals rather than #1 in prose.

Wrong: Our team is #1 priority for Q3.
Right: Our team is the No. 1 priority for Q3.
Wrong: She finished #1 in the class.
Right: She finished first in the class.

Hyphenation and number words (compound modifiers)

When a number word or phrase modifies a noun before it (a compound adjective), hyphenate. After the noun, don't hyphenate.

Before noun (hyphenate): a number-one hit, a five-year plan.
After verb (no hyphen): The hit was number one. The plan runs five years.
No. as an identifier: No. 1 candidate is an identifier, not a hyphenated adjective.

Correct: a number-one bestseller.
Correct: The bestseller was number one for three weeks.

Spacing, punctuation, and numeric formatting

Avoid writing "#500" or "# 500" in running text. Replace the symbol with a properly formatted numeral (500 or 1,000) or the word form per your style guide. Use commas for thousands in technical copy unless directed otherwise.

If you use No., keep the period and a space before the number (No. 4).

Don't use "# 123" in prose. Use "No. 123" or "123" depending on role.
Large numbers: write 1,000 rather than 1000 in many guides.
Punctuation: place commas and periods per sentence rules - "Issue No. 5, revised" is correct.

Wrong: The conference attracted an audience of #500 attendees.
Right: The conference attracted an audience of 500 attendees.
Wrong: Report shows #1000 sales in Q1.
Right: The report shows 1,000 sales in Q1.

Try your own sentence

Test the whole sentence, not just the phrase. Context usually makes the right form clear: read it aloud and pick the version that sounds natural.

Memory trick: two quick questions to pick the right form

Ask: (1) Is this a label/ID? (2) Is it a rank or a count? Those answers point to No., an ordinal, or a numeral/word.

If you're uncertain, read the sentence out loud-spoken phrasing reveals when a symbol is jarring.

Label/ID → No. or keep # only in technical contexts.
Rank/sequence → ordinal (first, second).
Count/fact → numeral with commas or spelled-out number per style.

Test: "They finished #2." Read aloud as "They finished number two." Better: "They finished second."

Examples - copyable wrong/right pairs for work, school, and casual use

Swap nouns or numbers as needed; keep punctuation consistent with your sentence. These examples cover work, school, and casual contexts.

Work - Wrong: Our team is #1 priority for Q3.
Right: Our team is the No. 1 priority for Q3.
Work - Wrong: Please send files to #2 client on the list.
Right: Please send files to the No. 2 client on the list.
Work - Wrong: The invoice shows #10 items and #2 discounts.
Right: The invoice shows 10 items and 2 discounts.
School - Wrong: Refer to #3 in the bibliography.
Right: Refer to No. 3 in the bibliography.
School - Wrong: She scored #95 on the math test.
Right: She scored 95 on the math test.
School - Wrong: Cite #2 paragraph in your analysis.
Right: Cite paragraph 2 in your analysis.
Casual - Wrong: Meet me at #5 coffee shop on Main St.
Right: Meet me at the fifth coffee shop on Main St.
Casual - Wrong: I ranked us #1 in the group chat.
Right: I ranked us number one in the group chat.
Casual - Wrong: I got #1000 followers overnight!
Right: I got 1,000 followers overnight!
Extra - Wrong: The product is #3 bestseller this month. Right: The product is the No. 3 bestseller this month.

How to fix your sentence: step-by-step rewrites

Steps: identify the role (label, count, rank) → choose No./number/ordinal → adjust hyphenation and commas → read aloud. For many occurrences, review each instance rather than a blind replace.

Use these templates as quick rewrites.

Label template: "No. X" - Case No. 7; Client No. 2.
Count template: "X" with commas - 1,000 users; 250 copies.
Rank template: ordinal or natural phrasing - finished second; the top priority.

Rewrite:
Wrong: The company secured #1 position in the market. →
Right: The company secured the No. 1 position in the market.
Rewrite:
Wrong: The committee placed #3 on the agenda. →
Right: The committee placed item No. 3 on the agenda.
Rewrite:
Wrong: They were #2 in the competition. →
Right: They finished second in the competition.
Rewrite:
Wrong: Release notes reference #234 error. →
Right: Release notes reference Error No. 234.
Rewrite:
Wrong: Add #4 to the shopping list. →
Right: Add item number 4 to the shopping list.
Rewrite:
Wrong: Promo: #1 deal of the day! →
Right: Promo: the number-one deal of the day!

Similar mistakes to watch for

Watch for mixing forms across a document, confusing hashtags with number signs, and inconsistent numeral styles. Also check whether small numbers should be spelled out in narrative prose.

Hashtag vs number sign: #travel (hashtag) ≠ No. 5 (label).
Pound sign confusion: # is sometimes called "pound" - avoid unclear phrasing like "call me at pound 5."
Style consistency: choose one approach for labels and counts and note it in a brief style rule.

Problem: Paragraph 1: #1. Paragraph 2: number one. - inconsistent; pick one form.
Problem: Tweet: "The pound sign # is confusing" - clearer: "The number sign (#) can be confusing across dialects."

FAQ

Can I use # in a formal report instead of No.?

Prefer No. or the word "number" in formal reports. Use # only for internal tracking codes or when your organization's style guide allows it.

Should I use No. 3 or 3rd in citations and bibliographies?

For bibliography entries or numbered lists, No. 3 works as a label. For ordinal descriptions in prose, use third. Always follow the citation style required for your work.

Is there a rule about spacing after the # symbol?

In UI labels you may see #123 with no space. In running prose avoid the symbol and use No. 123 or 123. Never use "# 123" in formal running text.

How should I write large numbers instead of using #?

Use numerals with commas (1,000) for technical writing. Spell numbers in narrative only if your style guide requires it. Replace "#1000" with "1,000" or "one thousand" depending on tone.

Is # acceptable in emails to colleagues?

For quick, internal notes where everyone understands the shorthand, # is usually fine. For external or mixed-audience emails, replace # with No., number, or a spelled-out ordinal for clarity.

Need a quick second look?

If you're unsure which form fits, paste the sentence into a grammar checker that flags symbol usage and suggests context-aware rewrites. For consistent team output, add a short line to your style guide on when to use No., ordinals, and when # is allowed.