Why do prescriptions say mcg instead of µg?

Because a handwritten µ can pass for an m, and mg is a thousand times more than µg. Safety bodies such as the Institute for Safe Medication Practices list µg as an error-prone abbreviation and ask for mcg instead. Outside medicine, µg is still the correct SI symbol.

Is uF the same as µF on a capacitor?

Yes. u is the plain-ASCII stand-in for µ, so 10 uF means 10 µF, and it turns up in parts lists and schematics that can't count on having a µ. Older capacitors are marked mfd or MFD for microfarad, which is also µF and not millifarad, even though mF is the proper SI symbol for a millifarad.

Why does uppercasing µg turn it into ΜG?

Unicode gives the micro sign an uppercase, and it's the Greek capital Mu, which looks exactly like M. So µg becomes ΜG, and lowercasing that later yields the Greek μ rather than the micro sign you started with. Unit symbols are case-sensitive anyway (mg and Mg are different units), so keep them out of any case conversion.

Why do names like ÁLVAREZ come out as ╡LVAREZ?

Text written in code page 850 is being read as code page 437, so every Á turns into this box piece. The same mix-up turns Â into ╢ and À into ╖, while lowercase letters like á and ñ come through fine because both sets keep them in the same place. Decode with the right table, for example `new String(bytes, "IBM850")` in Java.

Why does Alt+181 give ╡ or Á instead of µ?

Alt codes typed without a leading zero come from your PC's DOS code page, and neither of the usual ones has µ at 181: the US set shows the box piece ╡, the Western European one Á. Alt+0181 reads Windows-1252 instead and gives µ. Both DOS sets do carry µ at 230, so Alt+230 works too.

ASCII 181

Micro signBox T-junction pointing left, double horizontal

ASCII 181 is µ on Windows and ╡ in old DOS.

µ (Micro Sign) is byte 181 in Windows-1252, Unicode U+00B5. It's the SI prefix for one millionth: µm, µs, µg. It has a twin, the Greek small letter mu μ (U+03BC), which looks the same on screen. Unicode treats the micro sign as a compatibility character, so NFKC normalization turns µ into μ, and a search that doesn't normalize will miss entries typed with the other one. Uppercasing is the stranger trap. The capital of µ is the Greek capital Mu, which looks like a Latin M, so 'µm'.upper() in Python or text-transform: uppercase in CSS gives ΜM, and an all-caps label reads as if it said MM. Old DOS had µ too, at 230. In UTF-8 it's C2 B5, which misreads as Âµ. The HTML entity is µ.

╡ (Single Vertical, Double Left) is byte 181 in code page 437, the original IBM PC character set, and maps to Unicode U+2561. It's a mixed tee for the right side of a single-line box, where a double horizontal ═ (205) comes in from the left and meets the single │ (179). The HTML entity spells that out: in &boxvL;, lowercase v means a single vertical and capital L a double left branch. Code page 850 gave this byte to Á, so a screen drawn for 437 shows Á wherever the frame needed this piece. In UTF-8 it's E2 95 A1.

Latin LetterBox Drawing

Technical Details

Code Example

</>

#include <stdio.h>

int main(void) {
    /* On Windows (code page 1252) byte 181 is µ.
       Modern terminals expect UTF-8, so print the code point, not the byte. */
    printf("\u00B5\n");   /* UTF-8: C2 B5 */

    unsigned char b = 181;         /* the raw Windows-1252 byte */
    printf("%d 0x%02X\n", b, b);    /* 181 0xB5 */
    return 0;
}

Code Example

</>

#include <stdio.h>

int main(void) {
    /* Byte 181 is ╡ only on a console using code page 437
       (chcp 437 on Windows, or DOSBox). On a UTF-8 terminal the
       lone byte 0xB5 is invalid and prints as garbage, often �. */
    putchar(181);

    /* char is signed on x86, so a plain char holding 0xB5 is -75.
       Use unsigned char when you compare or index by byte value. */
    char c = (char)181;
    unsigned char u = 181;
    printf("\n%d %d\n", c, u);   /* -75 181 */

    /* Portable: print the Unicode character as UTF-8 instead. */
    printf("\u2561\n");          /* E2 95 A1 */
    return 0;
}

How to Type It

Windows: Hold Alt and type 0181 on the numeric keypad, with Num Lock on. The leading zero picks the Windows code page. Alt+230, without the zero, types it too. No numeric keypad? In Word, type 00B5 and press Alt+X.
Mac: Press Option+M.
Linux: In GNOME, or any desktop running IBus, press Ctrl+Shift+U, type b5, then Space. With a Compose key set up, press Compose, m, u.
Phone: The Greek keyboard's μ is a different character. Tap the character at the top of this page to copy it.

How to Type It

Windows: Hold Alt and type 181 on the numeric keypad, with no leading zero. US PCs insert ╡, but PCs set to code page 850, common in Western Europe, insert Á. No numeric keypad? In Word, type 2561 and press Alt+X.
Mac: Press Control+Command+Space to open the Character Viewer, then search for "box drawings vertical single and left double".
Linux: In GNOME, or any desktop running IBus, press Ctrl+Shift+U, type 2561, then Space.
Phone: Phone keyboards have no key for it. Tap the character at the top of this page to copy it.

Frequently Asked Questions

Because a handwritten µ can pass for an m, and mg is a thousand times more than µg. Safety bodies such as the Institute for Safe Medication Practices list µg as an error-prone abbreviation and ask for mcg instead. Outside medicine, µg is still the correct SI symbol.
Yes. u is the plain-ASCII stand-in for µ, so 10 uF means 10 µF, and it turns up in parts lists and schematics that can't count on having a µ. Older capacitors are marked mfd or MFD for microfarad, which is also µF and not millifarad, even though mF is the proper SI symbol for a millifarad.
Unicode gives the micro sign an uppercase, and it's the Greek capital Mu, which looks exactly like M. So µg becomes ΜG, and lowercasing that later yields the Greek μ rather than the micro sign you started with. Unit symbols are case-sensitive anyway (mg and Mg are different units), so keep them out of any case conversion.
Alt codes typed without a leading zero come from your PC's DOS code page, and neither of the usual ones has µ at 181: the US set shows the box piece ╡, the Western European one Á. Alt+0181 reads Windows-1252 instead and gives µ. Both DOS sets do carry µ at 230, so Alt+230 works too.

Frequently Asked Questions

Text written in code page 850 is being read as code page 437, so every Á turns into this box piece. The same mix-up turns Â into ╢ and À into ╖, while lowercase letters like á and ñ come through fine because both sets keep them in the same place. Decode with the right table, for example `new String(bytes, "IBM850")` in Java.
Alt codes typed without a leading zero come from your PC's DOS code page, and neither of the usual ones has µ at 181: the US set shows the box piece ╡, the Western European one Á. Alt+0181 reads Windows-1252 instead and gives µ. Both DOS sets do carry µ at 230, so Alt+230 works too.

ASCII 181

Micro signBox T-junction pointing left, double horizontal

ASCII 181 is µ on Windows and ╡ in old DOS.

Latin Letter

Box Drawing

#include <stdio.h>

int main(void) {

/* On Windows (code page 1252) byte 181 is µ.

Modern terminals expect UTF-8, so print the code point, not the byte. */

printf("\u00B5\n"); /* UTF-8: C2 B5 */

unsigned char b = 181; /* the raw Windows-1252 byte */

printf("%d 0x%02X\n", b, b); /* 181 0xB5 */

return 0;

}

#include <stdio.h>

int main(void) {

/* Byte 181 is ╡ only on a console using code page 437

(chcp 437 on Windows, or DOSBox). On a UTF-8 terminal the

lone byte 0xB5 is invalid and prints as garbage, often �. */

putchar(181);

/* char is signed on x86, so a plain char holding 0xB5 is -75.

Use unsigned char when you compare or index by byte value. */

char c = (char)181;

unsigned char u = 181;

printf("\n%d %d\n", c, u); /* -75 181 */

/* Portable: print the Unicode character as UTF-8 instead. */

printf("\u2561\n"); /* E2 95 A1 */

return 0;

}