A few weeks ago I mentioned I used Algebra to figure out the dimensions of the bags, totes, baskets, and boxes I design.
Today I’m demonstrating the calculations I use.
But first a little background….
Last month I said I was making a bag for my daughter-in-law’s school’s fall festival auction using these Premier Prints fabrics…
But I really messed up the pocket on the bag plus ran out of the gray thread that I was using. I was working on a very short timeframe so rather than getting the ripper out and then driving to Jo-ann’s which is 35 minutes away to get more thread, I pulled some other Premier Prints fabrics out of my stash and made this bag instead:
Then I put a little tutorial together that explained how I made the boxed corners for the bottom which gives the bag that nice structure.
And my daughter-in-law just texted me that the bag went for $50 at the auction!
I hate leaving anything unfinished before I move onto another project. The orange and gray fabric was sitting there nicely cut out and lined in fleece, it just needed a little TLC and I had already picked up more thread. So I decided to fix the pocket and create a new tote.
And here’s where the calculations come in….
I keep an Excel Spreadsheet on my computer with formulas in it just to figure out–quickly and easily–how to change the sizes on bags, totes, baskets and boxes.
My three variables are height (h), width (w), and depth (d).
I use 1/2″ seams on all my totes, bags, and boxes.
I want this tote to be 12 1/2″ in height (h), 13″ in width (w), and have a 4″ depth (d).
So I need a piece of fabric cut 35″ x 15 1/2″. And how did I know that?
To get the width, the calculation is ((2 * w) + (2 * d) + 1)
The 1 in the above formula is for the 1/2″ seam on the sides of the bag.
The desired width is 13″ and the depth is 4″ so I just fill in the variables.
(2 * 13) + (2 * 4) + 1 = 35
The height formula is (h + (1/2 * d) + 1)
Again, the 1 is for the seams on the top and bottom.
The height is 12 1/2″ and the depth is 4″
(12.5 + (.5 * 4) + 1) = 15.5
One last calculation allows me to figure out how to box the corners.
(d/2)
My depth on this bag is 4″
4/2 = 2″
Confusing? Not really. It’s easy-peasy. Especially if you put the formulas into Excel. But, I always liked Algebra–except those word problems.
And here’s the inside of the bag.
I don’t have any plans for this bag yet. Perhaps it will go into into my inventory so next time I get a last minute text that I need to make a bag–I’m ahead of the game!
You may also want to check out:
My brain is hurting so early ! (LOL – kidding)
Thanks for the formula! That’s what I always loved about algebra, because with formulas, you only have to plug in numbers. Getting ready, now, to calculate the measurements for a small purse.
I keep the formula in a spreadsheet and turn to that every time I design a new bag, tote, or box!
Thank you for this. I’m reteaching to myself to sew. I was injuring my brain trying to figure out how to calculate how to box corners for some boxes I’m going to make. I’m going to create a spreadsheet right now!
Glad you can use it!
HEy this is really useful thank you, would it be the same formula to use if I wanted to make a square box closed at the top with a zipper? So material forming a complete cube…. maths really wasn’t my strongest subject!
I think it would be. I haven’t made one with a zipper on top so I can’t really advise you on that one. I always liked math but I have this formula in an excel spreadsheet and just plug in the numbers whenever I need to make a new size!
Thanks a bunch for this information! Making 2 different sizes of fabric baskets for my daughters new boot bench. Was trying to calculate fabric needed for her to order. She wants me to make 3 of each, wish me luck!!
Hope the fabric baskets worked out, Jan! I have more sewing tutorials on my other blog, DesignsbyKTGreen.com. Thanks for reading and commenting.
Nice formula. You haven’t calculated / included the Handle fabric Consumption. But really useful.
Can you Teach me more in Calculating Fabric Consumption for Woven Cotton Madeups like Bags, Pillow Cases Etc…
Ramesh Kumar
India
I’m not sure what you need, Ramesh. I have many more tutorials on my other website, DesignsbyKTGreen.com. Including bags, pillowcases, etc. Thanks for reading and commenting.
Dear Spreadsheet Queen, There’s nothing I love more than an excuse to make a useful spreadsheet such as this. I’m so glad you provided the formulas for all three calculations required. I had been trying to work them out, via a bit of trial and error with fabric scraps, but was doing it in multiple steps versus one nice, beautiful, succinct formula such as yours. Brilliant work! Many, many thanks!!
So the next challenge is to reverse calculate the multiple dimension possibilities of a bag one can make with a fabric rectangle of known dimensions, like all those scraps in my closet! I’ll work on that later…..;-)
Dear Carol,
Thank you for reading my blog…and commenting!
I love numbers. Always did. Loved Algebra even though I was too lazy to study and get good grades. Still loved it. Love sewing even more so being able to use a little algebra in my favorite hobby is even more fun!
So happy you like my little formula and understand it. When I explained it to one person she gave me the “deer in the headlights” look! I just think it makes my sewing life a little easier!
I have been moving my tutorials over to my other blog DesignsbyKTGreen.com which is dedicated to sewing and other handiwork.
Kathy
hi…
Sorry but I don’t understand…
once I have determined the measures of the cut of the Fabric … I have to cut 2? or do I have to divide the piece in half?
I used the formula but the piece of fabric seems to me enormous for what I want to do…
I need a basket h 9″ w 5,5″ and d 5,5″… with the formula now I have a piece of fabric w 23″ h 12,75″…. for the basket, I usually use the “1 hour basket” tutorial from Kelbysews… help! ;(
Hi Giada!
I ran a calcuation with my formula and you have cut out the fabric correctly. It should be 23″ x 12.75″. You have to take into account the front and the back and two sides along with the amount for the bottom of the basket. If you are using just one fabric you will only need the one seam and box the bottom.
I have a sewing blog now and another post about how I made a basic boxed bag. You might want to check on that one, too. More pics. The link is https://designsbyktgreen.com/basic-boxed-bottom-bag-part-1/
I followed that up with some other ways to use more than one fabric on this post https://designsbyktgreen.com/hand-stitchery-bag-tutorial/
Good Luck and let me know how you do!
Thank you! This is exactly what I needed. I’m phasing out paper gift bags for our family Christmas in favor of cloth ones and wanted a formula to help me make sets in specific sizes.
Love this. I make lots of tote bags but always struggled. I love spreadsheets and so this made sense to me and I already made a spreadsheet to use. A question I have is when you make a tote bag are there any dimensions that look better than others or that are kind of standard? (relation of height to width)
Thank you! Just made a little spreadsheet that will be very helpful!
Thanks, I googled “calculate box corners” or some such and your page was one of the first hits! Now I’m dying to see more of your handy calculations!
Hi Lori, thanks for reading my blog. I have many more DIY posts on my other blog which is designsbyKTGreen.com.
Is that 35 inch width for the entire bag? jDo you just wrap it around with 1 side seam or do you then cut that in half to get 2 side seams making each side 17 1/2 inches .
Hi Nora, there is only one side seam on this bag. The bottom is stitched and then the corners boxed. You can see more detail on my DIY blog at this post: https://designsbyktgreen.com/basic-boxed-bottom-bag-part-1/. Thanks for commenting! Kathy
Thanks 1,000,000 this is just what I needed – I’ve set it up in excel too 🙂 I’m a bit addicted to making fabric boxes so this is perfect. Thank you!
I’m so glad you like my formulas! I rely on my Excel spreadsheet everytime I design a new bag, box, or tote.
This is great, thank you for sharing this. For those who need to use two panels instead of one long piece, would total width be calculated the same way by adding 2 for seam allowance instead of 1, then dividing that total by 2 to get the size for each panel. By panel I mean front and back pieces of fabric. I find it much easier to measure for the pockets and straps on a smaller panel than such a long one and it would also be easier for me to sew, less bulk under the machine. Thank you!
Hi Wendy, if you add a seam you have to add the seam allowance. My bags are usually 1/2″ seam allowances. So you have to add an inch for each panel. Thanks for reading my blog.
I know this is a very old post, but thank you so much for keeping it up! I’m working on a bag pattern that I want to make a little deeper than the designer called for. I knew I had to change all my cutting dimensions, but I wasn’t sure how to do it. Algebra to the rescue!
Thanks for taking the time to comment! When I first started designing my own bags, I just scratched everything down on a piece of paper. But I started to make so many in different sizes, I had to come up with a formula. I still use that spread sheet!
By the way, my more up to date posts are on my other website. DesignsbyKTGreen.com
As someone who really desires to write patterns but has only a self taught background, this info is so super helpful!
After a crash course in excel and help from my 20 YO I successfully plugged in the formula!
Here it is for any who still see this. And I am going to check out your new blog!
Width
In cell C1 enter =2*A1+2*B1+1
Height
In cell C2 enter =A2+(0.5*B2)+1
And thank you again for sharing this!!
So glad my formula helped you out! Now, if I could just figure out inset zippers!
I don’t know if this group is still active, but if anyone could help me, I would really appreciate it. Using the formula above, which I understand, what would I change if I am going to sew a makeup bag. What numbers would I add in if i am adding a zipper to the makeup bag?
I don’t know if this is the correct way. I make a lot of zippered pouches. I use this program. I figure that what you would fold over at the top on a tote bag would be about equivalent to what you would use when putting in a zipper. I don’t know that they come out exactly to the numbers I put in the spreadsheet, but they are close. Try making a small sample zippered pouch and see what happens. It will also depend on what size zipper you use. I also have duplicated the spreadsheet so that when I input my numbers I get outputs for seams of 1/4, 3/8 and 1/2 inch. Don’t know if this will help you or not.
Thank you so much for this great explanation! I truly appreciate it!
Thank you. I’ve used your spreadsheet for years.
I’m still checking emails and comments on this site but all of my newer sewing and crafting posts are now on DesignsbyKTGreen.com. Please see Jen Knaub’s excellent explanation of putting a zipper in. I do not typically put zippers in my bags but her response makes sense. I do put zippers in pouches. You can see my latest pouch post here: https://designsbyktgreen.com/perfect-pretty-pouches/
Thank you so much. I recently started designing my own crochet bags with liners, pockets, zippers, etc. Your formula is a lifesaver. My mom was the seamstress, not me….. but I determined.
I am so glad that my formula helped you out! I would love to see some of your crochet bags. I can crochet a little but have never tried bags.I have more bags, etc. on my other website. DesignsbyKTGreen.com