If you have inches but need millimeters, follow these steps:
In descending order of size…
1/16 inch Equals almost 2mm
1/8 inch = little more than 3mm
1/4 inch = little more than 6mm
3/8 inch Equals almost 10mm
1/2 inch Equals about 13mm
16mm Equals 5/8 inch
19mm Equals 3/4 inch
7/8 inch = slightly more than 22mm
1 inch equals 25.4mm
If you have millimeters but require inches, use the following formula:
1mm = little more than 1/32 inch
2mm = little more than 1/16 inch
3mm Equals almost 1/8 inch
4mm = 5/32 inch (= little more than 1/8 inch)
5mm = little more than 3/16 inch 6mm = about 1/4 inch
7mm = almost 9/32 inch (= somewhat more than 1/4 inch)
8mm is equal to 5/16 inch.
9mm Equals about 3/8 inch
10mm = little more than 3/8 inch
11mm is about 7/16 inch.
12mm = almost 15/32 inch (= about 1/2 inch)
13mm = little more than 1/2 inch
14mm = about 9/16 inch
15mm = about 19/32 inch
16mm is equal to 5/8 inch.
17mm = approximately 11/16 inch 18mm = little more than 11/16 inch
19mm = 3/4 inch; 20mm = 25/32 inch; 21mm = little more than 13/16 inch
22mm = about 7/8 inch
23mm = 29/32 inch 24mm = somewhat more than 15/16 inch 25mm = about 1 inch
If you have inches and wish to convert them to millimeters:
First and foremost, Convert any inch fraction to a decimal number.
1/4 inch = 1 divided by 4 equals 0.25 inch
For instance, 1/16 inch = 1 divided by 16 = 0.0625 inch
For quantities more than an inch, first convert the fractional component, then add the entire inch part:
For instance, 2-1/4 inch = 1 divided by 4, then added 2 = 2.25 inch
For instance, 1-5/8 inch is 5 divided by 8, then adding 1 equals 1.625 inches.
Step two is to multiply the decimal by 25.4.
The entire steps for each of the above cases would be:
1/4 inch = 1 divided by 4, multiplied by 25.4 = 6.35mm (6mm)
1/16 inch = 1 divided by 16, multiplied by 25.4 = 1.5875 (1.6mm)
2-1/4 inch = 1 divided by 4, plus 2, multiplied by 25.4 = 57.15 (57mm)
1-5/8 inch = 5 divided by 8, plus 1, multiplied by 25.4 = 41.275 (41mm)
If you have millimeters (or centimeters) and desire inches, do the following:
First and foremost, Divide your millimeter measurement by 25.4. (or divide your centimeter amount by 2.54)
2mm divided by 25.4 equals.07874 inches in Example 1.
6mm divided by 25.4 equals.2362 inches in Example 2.
30mm divided by 25.4 is 1.1811 inches in Example 3.
4cm divided by 2.54 is 1.5748 inches in Example 4.
You may use this decimal number directly to calculate how many 6mm beads you need for a 20″ necklace. You already know that a 6mm bead equals.2362 inches from Example 2.
So 20 inches divided by.2362 inches each bead equals 84.67 beads per necklace.
I’d round down to 80 beads since you’ll probably need some room for bead tips and a clasp. Chart illustrating the number of beads per strand
If you want fractions of an inch (1/16, 1/4, 1/2) rather than decimals, try this:
Step number two: How to convert a decimal to a usable fraction:
I like to round to the closest 1/16-inch increment. Multiply your decimal by 16 to get to the closest 1/16 inch. The result is the number of 1/16’s of an inch you have.
Using the figures from Step 1:
07874 divided by 16 is 1.26, which rounds to 1, or roughly 1/16 inch.
2362 divided by 16 is 3.779, which rounds to 4, or around 4/16. 4/16 inch Equals 1/4 inch
For quantities more than an inch, it is simplest to remove the whole inches and then reintroduce them after converting the section following the decimal point:
1.1811 By removing the 1, you get. 1811 divided by 16 is 2.9, which rounds to 3, or roughly 3/16 inch… don’t forget to put the 1 back in, for a total of 1-3/16 inch.
1.5748 By removing the 1, you get. 5748 divided by 16 equals 9.1968, which rounds to 9, or roughly 9/16 inch… don’t forget to put the 1 back in, for a total of 1-9/16 inch.
I don’t advocate rounding to greater fractions, such as 1/4 or even 1/8 inch, for jewelry reasons. If you are not producing jewelry or your requirements are not precise, you may round to a bigger fraction, such as 1/4. Simply replace all of the 16’s in Step 2’s examples with 4’s to round to the closest 1/4 of an inch.
Using the values from step 1, which I also used in step 2, you get….07874 times 4 =.315, which rounds to zero, giving you 0/4 of an inch (not a very helpful number!).
2362 multiplied by 4 equals.9448, which rounds to one and gives you a quarter-inch measurement (which happens to be accurate)
Conversion Numbers in Miscellaneous Forms
To Convert… inches to millimeters, multiply by 25.4 inches to centimeters, multiply by 2.54 millimeters to inches, divide by 25.4 centimeters to inches, multiply by 3.28 feet to meters, divide by 3.28 millimeters to centimeters, divide by 10 centimeters to meters, divide by 100 centimeters to meters