How to Size Press On Nails: Pick the Perfect Fit with the Size Up and File Down Method

If your press on nails ever pop off, snag your hair, or feel pinchy, the problem is usually not the glue. It is sizing.

The goal is simple: full side to side coverage without touching skin and without squeezing your nail plate. When fit is correct, nails look cleaner, feel comfortable, and stay on longer.

This guide teaches the most reliable rule for real life hands: Size up, then file down for a custom fit.

Why sizing matters for comfort, wear time, and nail health

A press on nail that fits well sits flush and creates even contact for adhesive. A nail that fits poorly can lift at the edges and create tiny gaps.

Those gaps matter because moisture can get trapped under artificial nails. Press on nails can trap moisture, creating a damp environment where fungus and bacteria can thrive.

Artificial nails can also carry more microbes than natural nails in research settings, which is one reason correct fit, clean prep, and reasonable length matter.

Quick fit outcomes

Too small
• Can feel tight or painful
• Often lifts faster because the tip is fighting your nail width
• May leave side gaps if it does not fully cover
Too large
• Can overhang onto skin and lift at the edges
• More likely to catch on hair and fabric
• Looks bulkier unless refined
Just right
• Covers the nail plate edge to edge
• Does not touch skin
• Feels secure, not squeezed

The method: Size up and file down

Size up and file down means you intentionally choose a nail that is slightly wider than your natural nail, then gently file the sides until it matches your exact outline.

Why this works better than forcing a smaller size

You can remove material, but you cannot add it back.
A slightly wider nail gives full coverage, which supports better adhesion.
It reduces the risk of side gaps where water can sneak in.
It prevents that tight “snap on” feeling that often leads to pop offs.

Step 1: Measure your nail width in millimeters

This is helpful if you ever have to shop and come across some design that need you select a size.

Measure the widest point of each nail from sidewall to sidewall. Measure both hands.

Option A: Tape method, most accurate at home

Place a strip of clear tape across the widest part of your nail.
Press the tape down into the sidewalls so it follows your natural curve.
Mark the left and right edges where the nail meets skin.
Remove the tape and measure the distance between the marks in millimeters.
Repeat for all 10 nails.

Option B: Soft measuring tape

Lay the tape across the widest part of your nail.
Read the width in millimeters and record it.
Repeat for all 10 nails.

Pro tip

Use thin marks and measure only the hard nail plate. Do not include skin or cuticle.

Step 2: Understand sizes: numbered tips vs preset kits

This is where many shoppers get confused.

Numbered sizes

Most press on nails use numbers molded under each tip, often with 0 as the largest and higher numbers as smaller tips. These are individual nail sizes.

Preset kits

Preset kits like XS, S, M, L are collections of numbered tips. A preset kit is not a single size. It is a common mix that fits many people.

Step 3: Use a simple reference table, then rely on dry fit

Sizes vary by brand and shape, but this table helps you start in the right neighborhood.

Table 1: Typical numbered sizes and approximate widths

Numbered size	Approximate width in mm	Common finger
0	16 to 18	Thumb
1 to 2	14 to 16	Thumb or index
3 to 4	12 to 14	Index
5 to 6	11 to 13	Middle
7 to 8	9 to 11	Ring
9 to 11	7 to 9	Pinky

Use this as a guide, then confirm with a dry fit on your actual nails.

Table 2: Common preset sets by width, approximate

Preset set	Thumb mm	Index mm	Middle mm	Ring mm	Pinky mm
XS	14	10	11	10	7
S	15	11	12	11	8
M	16	12	13	12	9
L	18	13	14	13	10

If you do not match a preset perfectly, that is normal. That is exactly why the size up and file down method exists.

Step 4: Dry fit test before any glue

Dry fitting prevents mistakes and wasted product.

Lay out your chosen nails by finger.
Place each nail on your finger without adhesive.
Align the bottom edge so it mirrors your cuticle curve, not sitting on skin.
Press lightly across the surface.

Your dry fit checklist

No side gaps
If you see natural nail on either side, the tip is too small. Size up.
No skin overlap
If the tip touches skin, it is too large, but it may still be perfect after filing.
No rocking
If the nail rocks when you press the center, the curve is not right. Try a different size.

Step 5: File down for a custom fit

This is where ShadePax sets start to look truly tailored.

What you need

• A nail file which is included in our package when you order any press on nail item from ShadePax.

How to file, step by step

Start with the nail you sized up to.
Hold it against your natural nail and identify where it overhangs.
File only the press on nail, focusing on the left and right side edges.
File in one direction with gentle strokes.
Test fit every few strokes.
Alternate sides to keep the shape symmetrical.
Smooth the edge with a buffer when it is perfect.

Optional refinements

• If the cuticle edge is slightly too round or too square for your cuticle line, lightly refine the bottom edge.
• If you prefer shorter nails or you are active with your hands, shorten the length to reduce leverage.

Shape specific tips

Different shapes fit differently even at the same width.

Almond

• Often feels tighter at the sides
• Size up more often
• File conservatively to keep the taper smooth

Coffin

• Width changes quickly as the sides taper
• Start by fitting the widest part of your nail bed, then file into the coffin shape

Square

• Easiest to file evenly
• Focus on sidewalls while keeping the tip straight

Round and oval

• Most beginner friendly
• Small filing changes blend naturally

Pro tips for longer wear and safer use

Prevent lifting and moisture traps

• Apply only on clean, dry nails
• Wipe the nail plate with alcohol and let it fully dry before adhesive
Moisture trapped under artificial nails can increase the chance of bacteria or fungus growth.

Be gentle with your natural nails

Artificial nail processes can thin and weaken natural nails due to filing and chemicals, so keep prep gentle and prioritize nail health between sets.

Handle nail glue carefully

Use a small amount, apply over a hard surface, and keep glue away from clothing and towels.

Common sizing mistakes to avoid

Choosing the smaller tip because it looks neat in the box
If it leaves side gaps or feels tight, it will usually lift faster. Size up.
Assuming both hands are identical
Many people have small differences. Measure both hands and build a real size map.
Skipping dry fit
Dry fit is the fastest way to catch errors before adhesive.
Over filing
Remove tiny amounts and test often. Once it is too narrow, you cannot fix it.
Confusing preset kits with numbered sizes
Presets are collections. Your best fit often uses a mix.