I'll walk you through the process of calculating
one quilt, using a 12" Starflower Block as the
Example. The Supplies List for that
pattern tells you that you need the following amounts for one
block:
Color
1

Color
1 needs: two strips 37/8" x 73/4" 
Color
2

Color
2 needs: two strips 37/8" x 73/4" 
Color
3

Color
3 needs: one strip 31/2" x 14" AND two
strips 37/8" x 73/4" 
If we are making a FULL sized quilt, and
doing BlocktoBlock construction (No Sashings) we will plan on
making 56 blocks, so will need 56 of each of the fabric units
needed. Our job is to figure out how many yards that means! There
are just FIVE STEPS:
Step One: First, multiply
the strips/units you know you need( shown above in the Supplies
List) times the number of blocks you plan to make ( 56):
For Color 1, two
strips 37/8" x 73/4" times 56 = we
will need 112 strips 37/8" x 73/4"
For Color 2,
two strips 37/8" x 73/4" times 56 = we
will need 112 strips 37/8" x 73/4"
For Color 3, one strip 31/2"
x 14" times 56 = we will need 56 strips 31/2" x
14"
AND two strips 37/8" x
73/4" times 56 = we will need
112 strips 37/8" x 73/4"
Step Two: Next, working with
one color at a time, find out how many full length strips/units
you can get from each 42" width of fabric you cut:
For Color 1, 42"
divided by 73/4" = 42divided by 7.75 = 5.42...so call it
FIVE (as .42 of a unit won't be long enough to use) (Always round
DOWN on this part!)
For Color 2, 42"
divided by 73/4" = 42/7.75 = 5.42...so call it FIVE (as .42
of a unit won't be long enough to use) (Always round DOWN on this
part!)
For Color 3, 42"
divided by 14" = 3THREE ( this came out exactlywe love
that!) for the first unit AND for the second
Color 3 strip, 42" divided by 73/4" = 42/7.75 =
5.42...so call it FIVE (as .42 of a unit won't be long enough to
use) (Always round DOWN on this part!)
Step Three: Next, still
working with one color at a time, divide the number of units you
NEED, by the number of units you can get from each strip you cut:
For Color 1, You NEED 112
(37/8" x 73/4") strips . You are going to get FIVE
from each 37/8" wide strip you cut... so 112 divided by 5 =
22.4 Call it 23 strips of that width you will need to
cut.( Always round UP on this part!)
For Color 2, You NEED 112
(37/8" x 73/4") strips . You are going to get FIVE
from each 37/8" wide strip you cut... so 112 divided by 5 =
22.4 Call it 23 strips of that width you will need to
cut.( Always round UP on this part!)
For Color 3, You NEED 56
(31/2" x 14") strips. You are going to get THREE from
each 31/2" wide strip you cut. 56 divided by 3 = 18.6 Call
it 19 strips of that width you will need to cut AND you
NEED 112 (37/8" x 73/4") strips . You are
going to get FIVE from each 37/8" wide strip you cut... so
112 divided by 5 = 22.4 Call it 23 strips of that
width you will need to cut.( Always round UP on this part!)
Step Four: Now, still
working with one Color at a time, MULTIPLY the number of
Strips you are going to cut times the width of each strip to find
out how many inches of fabric that is:
For Color 1, 23 strips x 3.875 =
89.125", or 89 1/8". Find the nearest real measurement =
90 inches of Color 1 you need to get your units
For Color 2, 23 strips x 3.875 =
89.125", or 89 1/8". Find the nearest real measurement =
90 inches of Color 2 you need to get your units
For Color 3, 19 strips x 3.5 =
66.5" Find the nearest real measurement = 67 inches of
Color 3 you need to get your first units, AND 23 strips x 3.875 =
89.125", or 89 1/8". Find the nearest real measurement =
90 inches of Color 1 you need to get your second units. 67 plus 90
= 157 inches to get all units needed.
Step Five: And now, still
working with one color at a time, DIVIDE the number of inches you
need by 36" ( one Yard) to find out how many YARDS you need:
For Color 1, 90" divided by
36" = 2.5 yards
For Color 2, 90" divided by
36" = 2.5 yards
For Color 3, 157" divided by
36" = 4.361 or 4.5 yards
Then when you go to buy your fabric you
may want to bump each figure UP a little to plan for errors, or
whatever. Add more if you want to make BINDING. Add more if you
want to add BACKING. Add more if you absolutely LOVE IT :o) 