To find a tank that works tucked into jeans and untucked with a skirt, measure the length of a top you already like and compare it with the rise of both bottoms. That gives you a better reference than the size letter alone.
Shop the Pink/Flamingo Micro-rib TankFind the length that does both jobs
Try your favorite top with the jeans and skirt you reach for most. Tuck it in, sit down, and stand back up. Then wear it untucked and see where the hem falls. If the fabric bunches under both waistbands, look for a shorter top. If it slips out as soon as you sit, compare with a longer one. Write down the length that worked before you shop.
Check the straps under your outer layer
The Fieldtime Pink/Flamingo Micro-Rib Tank has thick straps and a mid-length cut, and the product listing identifies Airlume cotton. Try a tank with your usual bra and the jacket or blazer you plan to layer over it. Reach forward and see whether the armholes sit comfortably and the straps line up the way you want.
Compare flat measurements before ordering
Use the Fieldtime micro-rib tank chart to compare garment length and width with a tank you own. Follow the diagram and measure the reference top flat without stretching it. For a casual outfit, try the pink tank with straight-leg jeans. For a second look, try it with a skirt and an open blazer.