This is a free pattern with video tutorial, and can be used for self drafting a custom sized mask as well.
From Mimi G Style:
THE BEST AND EASIEST DIY FACE MASK WITH POCKET FOR FILTER
HI DARLINGS! This time in our lives has been unreal and so scary. Several weeks ago I was overwhelmed with requests to make a tutorial for a FACE MASK. I did a step by step with a download for the PATTERN on my YOUTUBE CHANNEL but I thought I would post it here on the blog too.
I have almost 1.3 Million views on this video and have received so many emails from you guys telling me you have made 100 masks, 300 masks, 500 masks for donating, for friends and family and that makes me feel so happy that I was able to help in some very small way.
In case you missed it below is the video as well as a link to print a PRINTABLE PATTERN or a MEASUREMENT PATTERN that you can use to draw your own if you are unable to print. I have been asked about using the mask for kids and what I have done is decreased the percentage I use to print. For an adult, you print at 100% (actual size) and for kids, I minimize the size, you can do 80% for most kids ages 6-9 and maybe try 50% for infants or toddlers. Play with the percentage until you get a size that fits for your child.