To figure out your nail size, measure the widest part of each natural nail in millimeters, then match those measurements to a brand’s sizing chart. Most people fall between 8mm (pinky) and 17mm or 18mm (thumb), and you’ll need to measure all ten fingers since your two hands often differ.
Where to Measure on Each Nail
The widest point of your nail is typically where the nail bed meets the free edge, right around the midpoint of your nail plate. This is the only measurement that matters for sizing. Don’t measure closer to your cuticle or at the tip, both of which are narrower and will give you an inaccurate number.
Hold your measuring tool straight across the nail horizontally. Even a slight diagonal will add width and throw off your result.
Three Ways to Measure
Soft Tape Measure
A flexible fabric or sewing tape measure is the most straightforward option. Press it flat across the widest point of each nail and read the millimeter side (not inches). If the edge of your nail falls between two lines, round up to the next millimeter. An average thumb usually measures somewhere between 16mm and 18mm.
Transparent Tape Method
If you don’t have a soft tape measure, place a small strip of clear tape across the widest part of your nail. Use a pen to mark both edges of the nail on the tape. Peel it off, stick it to a flat surface, and measure between the marks with any ruler. One important detail: don’t include the pen marks themselves in your measurement. Thick marker lines can add 2 to 3mm of false width.
Sizing Kits
Many press-on nail sellers offer physical sizing kits, a set of numbered blank nails you try on each finger to find the best match. These remove the guesswork entirely. Some makers include a sizing kit with your first order, while others charge a small fee and ship one separately. Once you know your sizes from a kit, they’re on file for future orders.
Adjusting for Flat or Curved Nail Beds
Millimeter measurements assume a moderate natural curve to your nails. If your nail beds are noticeably flat, the press-on needs to be slightly wider to sit flush without lifting at the edges. Add 1mm to each measurement for flat nails, or 2mm if your nails are very flat. People with a steep natural curve generally don’t need to adjust at all since the standard measurement captures the fit well.
How Standard Sizing Charts Work
Press-on nails and full-cover tips use a numbered system where size 0 is the largest and size 9 is the smallest. A common scale looks like this:
- Size 0: 17mm
- Size 1: 16mm
- Size 2: 15mm
- Size 3: 14mm
- Size 4: 13mm
- Size 5: 12mm
- Size 6: 11mm
- Size 7: 10mm
- Size 8: 9mm
- Size 9: 8mm
To give you a frame of reference, a typical medium hand uses roughly size 1 for the thumbs, size 4 or 5 for the middle and ring fingers, and size 8 for the pinkies. But there’s a lot of individual variation, which is why measuring every finger matters.
Brand Sizing Is Not Always Consistent
While many brands follow a similar scale, the actual millimeter widths attached to each size number can differ. One brand’s size 0 might be 17mm while another’s is closer to 13.5mm. One popular brand, for example, lists its size 2 at 10.92mm, well below the 15mm you’d expect from the chart above. This means your “size 4” in one brand could be a completely different fit in another.
The safest approach is to keep your raw millimeter measurements written down and compare them directly to each brand’s specific chart rather than assuming a size number carries over. If a brand doesn’t publish millimeter equivalents, a sizing kit is worth the extra step.
When You’re Between Sizes, Size Up
If your measurement lands between two sizes, always go with the larger one. A slightly wide press-on can be filed down along the edges for a precise, seamless fit. A nail that’s too narrow can’t be made wider, and it will leave visible gaps along the sides of your nail bed that catch on things and weaken the adhesion.
How Nail Shape Affects Fit
Your width measurement stays the same regardless of shape, but the shape you choose can change how the nail feels and how forgiving the fit is. Square and coffin shapes have straight sides that run parallel to your natural nail edges, so width accuracy matters more. Even a small mismatch is visible. Almond and oval shapes taper along the sides, which is slightly more forgiving since the tapered portion sits beyond the widest part of your nail bed and small discrepancies blend in more easily.
Shape also influences practical length. Coffin nails generally look best at longer lengths because the flat, squared-off tip needs enough runway to taper. Almond nails work well at medium or long lengths, giving you more flexibility.
Recording Your Sizes
Once you’ve measured, write your results in a simple format you can reference later. List each finger with its millimeter width, keeping left and right hands separate. Something like:
- Left hand: Thumb 17mm, Index 12mm, Middle 13mm, Ring 12mm, Pinky 9mm
- Right hand: Thumb 16mm, Index 11mm, Middle 13mm, Ring 11mm, Pinky 9mm
Your nail width stays fairly stable over time, so you only need to do this once. If you also note the corresponding size numbers for brands you order from regularly, reordering becomes nearly instant.