Go Back  Quiltingboard Forums > Main
Math Question >

Math Question

Math Question

Old 11-29-2020, 01:47 PM
  #1  
Super Member
Thread Starter
 
osewme's Avatar
 
Join Date: Apr 2011
Location: Texas
Posts: 4,801
Default Math Question

I want to make a 12" (finished) Disappearing 9 Patch quilt top.
I have 2 yards of light fabric & 2 1/2 yards of dark fabric (each is 42" wide)
I want to make each square with 5 dark fabrics & 4 light fabrics. I will cut each square 4 3/4" in order to end up with a 12" finished block.
I want to use 5 (12" blocks) across the top & 6 (12" blocks down the side).
I don't plan on using any sashing or borders on the quilt.
Will I have enough yardage on hand to make 30 Disappearing 9 patch blocks for the quilt top?
I know this math problem is simple for a lot of people but I'm math challenged & can't for the life of me figure this out. I want to make sure before I start cutting into my fabric. I know I will loose inches by cutting the blocks & re-sewing them into the Disappearing 9 Patch.
Thanks for any help on this one.
osewme is offline  
Old 11-29-2020, 02:01 PM
  #2  
maT
Member
 
Join Date: Nov 2010
Location: Rochester, NY
Posts: 96
Default

Yes you will
cut blocks only need to be 4 1/2" x 4 1/2" for finished 12"
maT is offline  
Old 11-29-2020, 02:16 PM
  #3  
Senior Member
 
Join Date: Jan 2010
Location: Alberta, Canada
Posts: 827
Default

.already answered

Last edited by JanieW; 11-29-2020 at 02:18 PM. Reason: Someone answered while I was typing
JanieW is offline  
Old 11-29-2020, 03:54 PM
  #4  
Super Member
 
OurWorkbench's Avatar
 
Join Date: Mar 2015
Location: Denver, CO
Posts: 2,555
Default

Originally Posted by maT View Post
Yes you will cut blocks only need to be 4 1/2" x 4 1/2" for finished 12"
I think that would make the finished 9-patch to 12" not a DNP..

If the size of the finished DNP is to be 12" I believe it would need to start out with larger squares. According to http://raevenfea.com/quilting/disappearing-nine-patch/ "Unfortunately, some common block sizes, like 6″, 8″, and 12″, end up requiring the starting squares be cut to third-inches,measurement." There was a thread that actually wanted a finished 12 - not 12.5 as title indicated and found what worked for ljptexas was to start with 4 3/4" and ended up unfinished 12.5" https://www.quiltingboard.com/7509612-post9.html

Janey - Neat people never make the exciting discoveries I do.
Not affiliated with off-site link(s)
OurWorkbench is offline  
Old 11-29-2020, 05:44 PM
  #5  
Senior Member
 
Join Date: Jul 2019
Posts: 469
Default

I did the math and the computer ate my calculations before I could post them. But...what I figured out is that you have exactly the amount you need but no room for error in cutting. And I mean exactly, make sure you have the full 2.5 yards and full 2 yards of the light after pressing and straightening the edges of the yardage. This is assuming you have 40 inches WOF after cutting off the selvage edges.
sewingpup is offline  
Old 11-29-2020, 06:33 PM
  #6  
Super Member
Thread Starter
 
osewme's Avatar
 
Join Date: Apr 2011
Location: Texas
Posts: 4,801
Default

Originally Posted by sewingpup View Post
I did the math and the computer ate my calculations before I could post them. But...what I figured out is that you have exactly the amount you need but no room for error in cutting. And I mean exactly, make sure you have the full 2.5 yards and full 2 yards of the light after pressing and straightening the edges of the yardage. This is assuming you have 40 inches WOF after cutting off the selvage edges.
YIKES! I just re-measured my dark fabric & I only have 2 1/3 yds. and it's 42" wide.
My light fabric is 44" wide x 2 yds. long
osewme is offline  
Old 11-29-2020, 06:34 PM
  #7  
Super Member
 
OurWorkbench's Avatar
 
Join Date: Mar 2015
Location: Denver, CO
Posts: 2,555
Default

The way I figure you can get 8 (4 3/4") squares by WOF and 15 by LOF for 2 yards so that would make 120 (4 3/4") squares of the light fabric. (You need 4 light squares per block and want 30 blocks, therefore 120 light squares.)

The dark fabric 8 (4 3/4") squares by WOF and 18 by LOF for 2 1/2 yards would only give you 144 squares (see below for correction) rather than the 150 squares needed. (You need 5 dark squares per block and want 30 blocks, therefore 150 dark squares.)

WOF -- 40 divided by 4.75 = 8.421052632

LOF -- Light 72 divided by 4.75 = 15.15789474
LOF -- Dark 90 divided by 4.75 = 18.94736842
LOF -- Dark 84 divided by 4.75 = 17.68421053

Available Light squares of fabric 8 x 15 = 120 needed 4 x 30 =120
Available Dark squares of fabric 8 x 18 = 144 needed 5 x 30 = 150
Available Dark squares of fabric 8 x 17 = 136 needed 5 x 30 = 150

Janey - Neat people never make the exciting discoveries I do.

ETA the figures are based on the fact that the fabric is square, but there is a very slight wiggle room.

Last edited by OurWorkbench; 11-29-2020 at 06:50 PM. Reason: correction figures based on new measurements
OurWorkbench is offline  
Old 11-29-2020, 07:47 PM
  #8  
Super Member
 
Join Date: Jun 2010
Location: The Deep South near Cajun Country, USA
Posts: 4,769
Default

A couple of postings on the board about the D9P

http://www.quiltingboard.com/t-95621-1.htm

Sandy's version of DPN. (Disappearing 9 patch) pics in post #17 - Quiltingboard Forums
Barb in Louisiana is offline  
Old 11-29-2020, 11:27 PM
  #9  
Super Member
 
Join Date: Dec 2017
Posts: 1,293
Default

With your updated yardage information, you just barely have enough light fabric for your plan, but you do not have enough dark fabric for your plan. (After my walk through, I give you two alternatives, so you can skip to the end if you don't want to read the explanation of the calculations.)

Here's a walk through of how I calculated this.

1. How many blocks are needed? "I want to use 5 (12" blocks) across the top & 6 (12" blocks down the side)." This means 5 x 6 blocks, which is 30.

2. How many of each fabric per block? "I want to make each square with 5 dark fabrics & 4 light fabrics." So for light it is 4, and for dark it is 5.

3. How many total squares of each fabric?. Multiply the number of blocks (#1) with the number of squares per block (#2).
So for light it is 30 x 4, which is 120, and for dark it is 30 x 5, which is 150.

Now we start to figure out the length of each fabric you need.

4. Measure the usable WOF - I will assume that your selvedges are 1" wide on each side. So the light WOF is 42 and the dark WOF is 40.

5. How many squares can be cut from a WOF strip? Take the WOF measurement (#4) and divide by the square size (4.75) and then round the number down to the nearest whole number. So for light it is 42 / 4.75 = 8.84, which rounds down to 8, and for dark it is 40 / 4.75 = 8.42, which rounds down to 8.

6. How many strips of each fabric do you need? Take the total squares of each fabric (#3) and divide it by the number of squares in a WOF strip (#5), and then round the number up to the nearest whole number. So for light it is 120 / 8 = 15 (no rounding needed), and for dark it is 150 / 8 = 18.75, which rounds up to 19.

7. What length of fabric do you need? Take the number of strips of each fabric (#6) and multiply by the square size (4.75). So for light it is 15 * 4.75", which is 71.25", which is just barely less than the 2 yards (72") that you have.
For dark it is 19 * 4.75", which is 90.25", which is more than the 2 1/3 yards (84") that you have. So you do not have enough dark fabric for your plan.

Alternatives:

A. Do you want to make a quilt with fewer blocks instead?

You have enough dark fabric to cut fabric to cut 17 WOF strips, which would give you 136 squares, which would allow you to make 27 blocks. So you could make a quilt with 6 blocks by 4 blocks.

B. Do you want to make a quilt with smaller blocks instead?

If you switch to cutting all your squares 4.25" inches, you can get 9 squares per WOF strip, so you need fewer strips (17 for dark) plus each strip is narrower, and so you need only 80.75" of the dark fabric. Cutting your squares 4.25" will give you a finished block size of 10.75". (Or you can cut all your squares 4" inches, and get a finished block size of 10". I got the information on calculating block size here.)
platyhiker is offline  
Old 11-30-2020, 05:48 AM
  #10  
Power Poster
 
Join Date: May 2008
Location: MN
Posts: 23,363
Default

The theoretical finished size of a disappearing nine patch block using nine 4.75 inch squares would be 12.25 inches.

The theoretical finished size of a disappearing nine patch block using 4.625 (4-5/8) inch squares would be 11.875 (11-7/8} inches.

The theoretical finished size of a disappearing nine patch block using 4.50 inch squares would be 11.50 inches.

Assuming 1/4 (0.25) inch seam allowances.

Last edited by bearisgray; 11-30-2020 at 06:04 AM.
bearisgray is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


FREE Quilting Newsletter


SEO by vBSEO ©2011, Crawlability, Inc.