Most hairpin lace patterns will specify the gauge that your strip should be crocheted at. By following the gauge, you ensure that you will acheive a similar fabric drape and size to the garment pictured in the pattern, as well as use the same amount of yarn as the pattern indicates. Keep changing the size of your crochet hook until you acheive the gauge that the pattern calls for.
Work a strip on the hairpin loom that is at least 4" long. Tie off and remove the strip from the loom. Lay the strip on a flat surface and make sure that the strip is relaxed but not stretched. Hairpin lace strips are very elastic, it is easy to over-stretch or compress them. Give your strip a slight tug on both sides and then smooth flat.
Measure the amount of loops within a 4" space on your strip. Your count will include the loops from both sides of the strip. Lay your gauge measure at just under the center line of stitches and measure. The example to the right has 27 loops in 4".