The front and back of the sleeve with cover both sides, and they will also help cover the sides. So on the flap side we only need one of the sides to be covered with the sleeve and since the top and bottom will both contribute, only half the needed measurement needs to be added. 1 side needed = 1/2 a side added to the measurements.
On the side without the flap, we need both sides to be covered by the sleeve, and since top and bottom contribute equally, only half the needed measurement needs to be added. 2 sides needed = 1 side added to the measurement.
Use a piece of printer paper for making your template. Set the case on the corner of paper. Mark the boundaries
Add the depth of the sides. 1/2 the depth for side opposite the flap. A full depth for other edge to the be cut.
Put the sleeve over the paper. Use a weight to keep it from moving around.
Use the tape to align the edge on the impulse bag sealer
Set the heat high so it melts the plastic enough that you can pull it apart while it's being sealed.
Then rotate and do the side of the sleeve.
Now you have a perfect sized resealable sleeve.
For thick items, you might want to put a small piece of tape at the top of the side you cut where the flap is. This will keep the extra pressure from starting a tear on the side. Can remove the tape carefully afterwards or just leave it there....it's not noticable.
Another custom sleeve I made for very thin CD cases. Started with a standard sleeve for a jewel case and cut it down to size.
