Cross Stitch Gauge by YarnTree
From the YarnTree website:
"Cross Stitch Gauge. Best stitch gauge ever! This fabulously handy Cross Stitch Gauge has gauges for all your stitch counts: 11, 14, 16, 18, 22, 25, 26, 28, 30, 32, 36, and 40. Three openings across this 3”x10” tool makes it easy to count your fabric. Also has rulers for inches, as well as centimeters, so if you know you have 50 stitches, you can tell how many inches that will be when stitched on different counts of fabric just by looking at your gauge. Made of durable white plastic and printed with black ruler markings. (use #1) you simply lay it on your fabric and see where the markings line up with the fabric threads
to find the count of your fabric.
(use #2) If your chart says the design is 80 stitches wide, you look for
the 80 marking on each stitch count slot, and that will show you how
large 80 stitches is in each count on the ruler.
(use #3) Say your chart is 170 stitches tall x 90 stitches wide and you
like to start stitching at the top, not in the middle. Use the cross
stitch gauge to find where the top of your design is. Place the correct
count gauge slot with 0 (zero) at the center of your fabric and the
numbers to the top, look where 85 falls (as 85 is 1/2 of 170) and that would be the top line
of your design.
If you like to start stitching in the top left corner of the design, as
many do, you may use the gauge to find the left border of the design as
well, by placing the correct fabric count slot horizontally at 0 and
finding 45 (which is 1/2 of 90). Manually follow up that row vertically
to find the intersection with the top of your design and that will be
where to start stitching."