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Estimates & Approximations
- (without a calculator)
If you have the inches,
and need to know the millimeters:
In order of increasing
size...
- 1/16 inch = almost
2mm
- 1/8 inch = just
barely over 3mm
- 1/4 inch = just
barely over 6mm
- 3/8 inch = almost
10mm
- 1/2 inch = almost
13mm
- 5/8 inch = 16mm
- 3/4 inch = 19mm
- 7/8 inch = just
barely over 22mm
- 1 inch = 25.4mm
If you have the millimeters,
and need to know the inches:
- 1mm = just over
1/32 inch
- 2mm = just over
1/16 inch
- 3mm = almost 1/8
inch
- 4mm = 5/32 inch
(= a bit over 1/8 inch)
- 5mm = just over
3/16 inch
- 6mm = almost 1/4
inch
- 7mm = almost 9/32
inch (= a bit over 1/4 inch)
- 8mm = 5/16 inch
- 9mm = almost 3/8
inch
- 10mm = just over
3/8 inch
- 11mm = almost 7/16
inch
- 12mm = almost 15/32
inch (= almost 1/2 inch)
- 13mm = just over
1/2 inch
- 14mm = almost 9/16
inch
- 15mm = almost 19/32
inch
- 16mm = 5/8 inch
- 17mm = almost 11/16
inch
- 18mm = just over
11/16 inch
- 19mm = 3/4 inch
- 20mm = 25/32 inch
- 21mm = just over
13/16 inch
- 22mm = almost 7/8
inch
- 23mm = 29/32 inch
- 24mm = just over
15/16 inch
- 25mm = almost 1
inch
Calculator
Conversions
If you have inches,
and want to know how many millimeters:
Step one: Convert
any inch fractions to decimals.
Example: 1/4
inch = 1 divided by 4 = .25 inch
Example: 1/16 inch = 1 divided by 16
= .0625 inch
For amounts over
an inch, you want to first convert the fractional part,
then add the whole inches part:
Example: 2-1/4
inch = 1 divided by 4, plus 2 = 2.25 inch
Example: 1-5/8 inch = 5 divided
by 8, plus 1 = 1.625 inch
Step two: Now multiply
that decimal by 25.4
For each of the above examples, the complete steps would be:
1/4 inch = 1 divided by 4, x 25.4 = 6.35mm
(6mm)
1/16 inch = 1 divided by 16, x 25.4
= 1.5875 (1.6mm)
2-1/4 inch = 1 divided by 4, plus 2,
x 25.4 = 57.15 (57mm)
1-5/8 inch = 5 divided by 8, plus 1,
x 25.4 = 41.275 (41mm)
If you have millimeters
(or centimeters), and you want inches:
Step one: Divide
your millimeter amount by 25.4
(or divide your centimeter amount by 2.54)
Example 1: 2mm divided by 25.4 = .07874 inches
Example 2: 6mm divided by 25.4 = .2362
inches
Example 3: 30mm divided by 25.4 = 1.1811
inches
Example 4: 4cm divided by 2.54 = 1.5748
inches
If you are trying
to figure out how many 6mm beads you need for a 20" necklace,
you can use this decimal value directly. From Example
2 above, you know that a 6mm bead = .2362 inches.
So, 20 inches (per
necklace) divided by .2362 inches (per bead) = 84.67
beads per necklace. Since you probably need to reserve
a bit of space for your bead tips and a clasp, I would
round down to 80 beads.
If, however, you want
fractions of an inch (1/16, 1/4, 1/2), rather than a
decimal, try this:
Step two: Converting
your decimal to a useable fraction:
I prefer to round to the nearest 1/16 of an inch. To round to
the nearest 1/16 of an inch, multiply your decimal by 16. The resulting
number is how many 1/16's of an inch you have.
Using the numbers
from Step 1 above:
.07874 times 16 = 1.26, which rounds to 1,
so about 1/16 inch.
.2362 times 16 = 3.779, or rounds to 4, so
about 4/16. 4/16 = 1/4 inch
For amounts over an
inch, it is easiest to remove the whole inches, and add
them back in after you convert the portion after the
decimal point: 1.1811 Removing
the 1 gives you .1811 times 16 = 2.9, which rounds to
3, so about 3/16 inch... don't forget to add the 1 back
on, so this is really 1-3/16 inch.
1.5748 Removing
the 1 gives you .5748 times 16 = 9.1968, which rounds
to 9, so about 9/16 inch... don't forget to add the 1
back on, so this is really 1-9/16 inch.
For jewelry purposes,
I don't recomend rounding to larger fractions, such as
1/4, or even 1/8 inch. If you are not making jewelry,
or your needs are not very exact, then you can round
to a larger fraction such as 1/4. To round to the nearest
1/4 of an inch, simply replace all the 16's in Step 2's
examples with 4's.
Using the numbers from step 1, that I also used in step 2, you would get...
.07874 times
4 = .315, which rounds to 0, or 0/4 of an inch (not a very
useful number!)
.2362 times 4 = .9448, which rounds
to 1, or 1/4 of an inch (which happens to be
accurate)
Miscellaneous
Numbers For Conversions
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, divide by 2.54
- meters to feet,
multiply by 3.28
- feet to meters,
divide by 3.28
- millimeters to
centimeters, multiply by 10
- centimeters to
meters, multiply by 100
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