When writing measurements, especially in the United States where the imperial system is common, you will often see symbols like ′ and ″. These marks represent feet and inches, respectively. But what exactly is the correct symbol for inches? Is it the same as quotation marks? Let’s break it down.
The Correct Symbol for Inches
The proper symbol for inches is the double prime character: ″ (Unicode U+2033). It looks similar to a quotation mark but is technically different in typography.
- Feet → Single prime:
′(Unicode U+2032) - Inches → Double prime:
″(Unicode U+2033)
So, a person who is five feet six inches tall would be written as: 5′ 6″.
Common Examples of Inch Notation
- 12″ = twelve inches
- 8′ 2″ = eight feet, two inches
- 3″ screw = a screw three inches long
- 15″ laptop = a laptop with a 15-inch screen
Why Not Use Quotation Marks?
Many people type regular straight quotes (") to indicate inches, but this is actually a shortcut or substitute for the real symbol. The true typographic character is the double prime, not quotation marks. While most readers understand both, using the correct symbol is considered more precise and professional in technical writing.
History of the Inch Symbol
The inch symbol evolved from a system of primes used in mathematics and measurement. The single prime (′) was used to mark minutes of arc and later adopted for feet. The double prime (″) followed naturally for inches, representing a smaller unit. This system provided a quick, compact way to show measurements without writing full words.
Over time, the prime symbols became standard in drafting, carpentry, architecture, and any field that deals with measurements in the imperial system. Today, they remain common in blueprints, technical documents, and product specifications.
How to Type the Inch Symbol
Depending on your device or software, typing the correct inch mark can be a bit tricky. Here are some methods:
Windows
- Hold
Altand type8243on the numeric keypad for ″ (double prime). - Hold
Altand type8242for ′ (single prime).
Mac
- Press
Option+Shift+]for ″ (double prime). - Press
Option+]for ′ (single prime).
HTML / Unicode
- Double prime (inches):
″or″ - Single prime (feet):
′or′
Copy-Paste
You can also simply copy and paste the characters:
- Single prime (feet): ′
- Double prime (inches): ″
Inches in Different Contexts
Everyday Use
In casual writing, you’ll often see the straight quote (“) used for inches. For example: “12” ruler.” Most readers understand this, but technically the symbol is incorrect.
Technical Documents
In fields like architecture, carpentry, and engineering, the correct use of primes is important for clarity. Ambiguity can lead to costly mistakes. For example, confusing feet and inches on a blueprint could result in major construction errors.
Digital Devices
Screen sizes for laptops, tablets, and TVs are typically measured diagonally in inches. Marketing materials often use the straight quote, e.g., “15″ display,” but the correct form is “15″ display.”
Common Mistakes to Avoid
- Using quotation marks instead of double prime — While widely accepted, it’s not the correct symbol.
- Forgetting to include the foot symbol — Writing “6 2″” without the prime for feet is ambiguous. The correct way is “6′ 2″.”
- Mixing units — Don’t write “6 inches′” or similar; keep symbols consistent.
Comparison Table: Symbols vs Words
| Measurement | Correct Symbol | Written Out |
|---|---|---|
| Five feet, six inches | 5′ 6″ | 5 feet, 6 inches |
| Twelve inches | 12″ | 12 inches |
| Eight feet, two inches | 8′ 2″ | 8 feet, 2 inches |
| Fifteen-inch laptop | 15″ | 15-inch |
FAQ
Is it wrong to use quotation marks for inches?
It’s not technically correct, but it is widely used in informal writing. In professional or technical contexts, you should use the double prime (″).
What symbol is used for feet?
The single prime (′) is used for feet. For example, 6′ 2″ means six feet, two inches.
Can I write “in” instead of using the inch symbol?
Yes, in less formal contexts you can simply write “12 in.” instead of “12″.” This is sometimes clearer for international audiences who may not recognize the symbol.
Why is it called a prime?
The prime symbol originated in mathematics and astronomy, where it was used to mark derivatives and minutes of arc. Over time, it was adopted for measurement shorthand.
Conclusion
The correct symbol for inches is the double prime (″), not a quotation mark. Feet are represented with the single prime (′). While quotation marks are often used as a shortcut, using the proper characters ensures accuracy, professionalism, and avoids confusion — especially in technical or academic contexts.
So whether you’re drafting a construction plan, writing a product description, or just texting a friend about your height, remember: 5′ 6″ is the proper way to write five feet six inches.
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