Femometer Sizing Kit Review: Everything You Need to Know Before Buying

Quick Verdict

The femometer sizing kit is not glamorous. It won't track your sleep or measure your temperature. What it will do is save you from the all-too-common mistake of ordering a femometer smart ring in the wrong size. If you're serious about trying the femometer smart ring — the temperature-tracking, fertility-monitoring ring that's been gaining traction — this sizing kit is a non-negotiable first step. Buy the sizing kit here, confirm your size, then order the ring. It's that straightforward, and skipping it almost always leads to regret.

What Is the Femometer Sizing Kit?

The femometer sizing kit is a plastic ring sizer that helps you determine your correct femometer ring size before you commit to buying the actual smart ring. Let me be direct: this is not the smart ring. It's a measurement tool made from sturdy plastic, designed to replicate the fit of the real thing. The actual femometer smart ring — which uses oxidised ceramic on the outside and a scratch-resistant inner coating — comes in sizes 6 through 9, and those sizes don't align with standard US ring sizing that you'd find at a jewellery store.

When I first looked into the femometer smart ring for personal use, I almost skipped the sizing kit entirely. It seemed like an unnecessary step and an extra delivery to wait for. Then I read enough return-policy reviews to change my mind. People who guessed their size based on existing rings or standard sizing often ended up with something too tight or too loose. The ceramic construction and internal sensors add thickness that standard rings don't have, so your usual size almost certainly won't apply.

Key Features

• Four sizes included (6, 7, 8, 9) — covers the full femometer ring range
• Plastic construction mirrors the real ring's profile and thickness
• Engraved numbers face the back of the hand for correct orientation
• Designed for index, middle, and ring finger placement
• 24-hour wear recommendation to confirm true fit
• Compact kit ships in a small padded envelope
• High-quality plastic maintains shape through multiple fittings

Hands-On Review

I ordered the sizing kit on a Tuesday and had it by Thursday — standard Prime shipping, no surprises. The kit itself is modest: four plastic rings labelled 6 through 9, held together on a small card. The plastic is solid, not flimsy. It doesn't bend when you're trying to slide it on, and it holds its shape overnight, which matters when you're doing the full 24-hour test.

Using it is simple enough in theory. Hold the sizer firmly against the base of your finger. It shouldn't rotate freely once seated — if it spins easily, go up a size. Wear it for at least 24 hours. Check how it feels during sleep, during a workout, when your hands are cold versus warm. I tested size 8 first and it felt fine during the day, but by bedtime I noticed it was snug in a way that made me hesitant to sleep in it. I switched to the 9 for the second day and the difference was immediately noticeable — more comfortable, no pressure, still secure enough that it didn't slide around.

What surprised me was how much the orientation mattered. The instructions say the engraved numbers should face the back of your hand. At first I thought it was cosmetic, but the ring sits differently when oriented correctly versus flipped around. The numbers are your cue that you're wearing it the intended way, which apparently affects sensor contact and reading accuracy.

The one thing nobody tells you in the product listing: your dominant hand might be a different size than your non-dominant hand. I measured my left hand first, then checked my right out of curiosity. Half a size difference. The kit doesn't come with eight pieces so you can test both hands simultaneously — you'll need to do one hand at a time, which extends the process if you're being thorough.

Who Should Buy It?

• Anyone planning to buy the femometer smart ring — this is the prerequisite step. No exceptions.
• Women interested in fertility tracking who want to confirm ring comfort before relying on it for temperature data overnight.
• People between standard ring sizes — if you normally wear a 7.5, you won't know whether to try 7 or 8 in the femometer without the kit.
• Heavy ring wearers who need to confirm a smart ring won't interfere with daily activities or sleep.

Skip this kit if you already own a femometer ring and know your size, or if you're just curious about the concept and not actually planning to buy the ring. The sizing kit is useless on its own — it doesn't track, monitor, or do anything except help you find your size.

Alternatives Worth Considering

Oura Ring Sizing Kit — if you're considering multiple smart rings, Oura also offers a sizing kit. The Oura ring is thicker and targets a different market (general wellness versus fertility focus), but the sizing process is similarly essential before purchase.

Local Jeweller Fitting — some jewellers will help you find your ring size using standard metal sizers. This won't give you a precise femometer size, but it can help you understand whether you're a 7, 8, or 9 in the ballpark before ordering the kit.

Direct From Femometer — if you already know your femometer size from a previous kit, you can skip this step entirely and go straight to the ring on Amazon. But if you're unsure, don't guess.

FAQ

Final Verdict

The femometer sizing kit is unglamorous, inexpensive, and absolutely necessary if you're buying the femometer smart ring. There's no clever technology here — just four pieces of well-made plastic and a clear set of instructions. The 24-hour wear test feels like a long wait when you're eager to start tracking, but it's the only way to know for certain that your ring will stay comfortable through sleep and daily life. I was initially frustrated by the extra step, but after reading about the return hassle people faced with wrong sizes, the sizing kit felt like cheap insurance. If you want the femometer smart ring, start here.