You can also make this as a no sew using fleece (fleece does not fray, woven fabric does so you cannot do a no sew with a woven). To make as a no sew you will need to add 4" to both sides of the hood and sides. Once you add those 4" you will not do any of the sewing, you will instead cut 1"-2" strips on both sides of the body pieces and hood pieces. Lay the carrier between the 2 body pieces and then tie 1 strip from the front piece to 1 strip from the back piece everywhere except where the carrier straps need to come out. Where the carrier straps need to come out you will just cut off the strips. That leaves only the tie downs at the bottom of the carrier to worry about. You can either do the variation that covers the waist strap and add 4" to that and tie around that, though you would have to untie to remove it. Or do the cover the waist strap version, adding 2" to the back and 1" to the front. Buy stick on velcro and stick it onto the extra and wrap around and velcro closed. Or you can cut a hole at least 1" from the edge of the bottom and tie your ribbon onto that.
To start you need the carrier you are making it for, you can use measurements as well but having the carrier handy is a good visual. Lay the carrier out and measure the carrier across at the widest point. For a carrier with seat darts this will not be at the waist. Add about 1.5" for 1/2" seam allowances and 1/4" topstitching.
Then measure from the bottom of the waistband to the top of the carrier. If your carrier has a hood and you want your cover to have a hood you need to have that on/out and measure to the top of that instead. If your carrier does not have one and you want one, measure your child's hat or coat hood (or child) and add several inches for growth room and if the carrier does not come up as high on them as a coat would. This is the size you need for a carrier that does NOT cover the waistband. The extra length is going to accomodate for when the seat is filled in by child, any stretch, and any seat darts. If you want the carrier to also cover the waist band you will need to measure the height of the waistband and add that. Or you can measure the carrier 3D instead of flat, meaning measure from the bottom of the waistband, into the seat dart, and up to the top. Whichever method you use, if you are doing around the waistband you will then need to add 2" to accomodate the velcro or snaps.
Now cut 2 pieces of fleece to the height and width you just determined with your measurements and adding. Fold that in half so the sides are even. Lay a childs coat or jacket hood on top (or you can use a plate) and cut a round portion out at the TOP ( if your fabric has an up and down you need to pay attention to this) FOLDED edge.
Next open the fabric back out flat. Next you need to look at your shoulder straps. Most are attached at an angle. Lay your carrier, lined up and atop your fleece. Mark where your angle is, keeping in mind you will also have an extra 3/4" for seam allowance and topstitching, as well as possibly more if your carrier is not as wide at the straps. Therefore your carrier will not be flush against the side of the fleece. It needs to be centered instead. Cut at an angle along the mark then cut up into the hood angling so that you are going back out to meet the full width (or your hood will be too small at the top). For symetry I then fold it back over and cut exactly the same from the other side but you can also just repeat this for the other side, Your resulting 2 pieces will look similiar to this (sorry, all 3 times I forgot to take a picture and I'm a bad artist).
Fold it back in half so the sides match again, right sides together. Sew from the back of the hood (what looks like the top middle of the "heart" on top of the diagram above) forward to the front of the hood (the edge along the side). Repeat for other body pieces. Opened up (with the hood top folded down to lay flat) and laid out this is what it will look like now.
Place right sides together I pin the corners together, then the seam of the hood. Then to mark where I do NOT sew I also pin on each side of the hole for the webbing on the body. You know the angled portion isn't sewn because it is the shoulder strap hole. But to determine where the webbing will be be, measure your carrier, from the body of the waist to the bottom of where the webbing meets the body. Make the hole wide enough to fit the BUCKLE. If you made it to cover the waistband too, measure the waistband, add 2" and mark each side with a pin.
Once pinned sew from 1 bottom edge (or pin) up to the pin marking the webbing hole. Then sew from the top of the webbing hole to the angled area for the shoulder straps. Repeat for the other side. Then sew around from the top of one shoulder strap hole, around the hood to the top of the other. Turn right side out and smooth.
If you made it to cover your waistband, now attach velcro or snaps to close the bottom. If you made it to not cover your waistband you need to attach ties or straps to keep it from riding up too high. You can use ribbon, bias, finished fabric, etc. I made this one with snap straps, I attached the snaps to ribbon. The finished project picture I made with tied ties. Measure your waistband and add an inch, cut 6 ribbons that length. If you want them to tie on, add enough to be able to tie them, cut 6. Pin one on each body piece, for a clean edge fold the bottom up about 1/2" before you pin. Pin them next to the side seams and in the center.
Topstitch around the bottom edge making sure the entire edge is folded up about 1/2". At the ribbons backstitch and restitch so you have a total of 3 (or more) lines of stitching there to reinforce the attachment.
I then topstitch, this helps keep it in place and smooth. I sew 1/4"-1/2" in from the side seam. Sew from where you started at the bottom (or pin), to your hole for the webbing. Then from the top of the hole to the bottom of the shoulder strap hole. Repeat for other side. DO NOT topstitch closed your holes. Topstitch around from the top of the shoulder strap hole, around the edge of the hood to the other shoulder strap hole. Now place your carrier with the hood down, stuffed, or removed, atop the cover matching up the shoulder straps to the holes. Mark the top of your carrier. Top stitch along that marking. This will keep the carrier from sliding down too much.
Contrastly, if you use the hood a lot you can mark where the hood straps are and leave holes open for those in the hood, as you did for the shoulder straps and webbing, when you are sewing and again when top stitching so the hood is covered but usable for sleeping.
Now attach velcro or snaps to your straps if you didn't make them long enough to tie. Stick it on and cuddle a baby.
This is my first tutorial and I didn't take near enough pictures. So if anything is unclear let me know. If anyone makes the no sew version and takes pictures and posts them let me know and I'll be happy to link to it. I promise next weeks will be better.