uni-ball one vs one F vs one P: Which Model Should You Buy?

If you've been curious about the uni-ball one series, you've probably noticed there are now three different models on the market. The standard one, the one F, and the compact one P each serve different purposes, and understanding these differences will help you pick the right pen for how you actually work.

I've used all three versions extensively at my desk here in Tokyo, and I want to walk you through the practical differences between them. This isn't about which is "best" because that depends entirely on your writing habits and what you need a pen to do.

The original one launched the entire lineup and comes in the widest variety of colors and tip sizes. You can get it in 0.38mm, 0.5mm, or 0.7mm, and there are over twenty-five colors available in the 0.38mm size alone.

The standard one has a firm rubber grip section, which gives you traction when writing. The pen body is minimalist with a small tab and ring near the push button that matches your ink color. It's lightweight and comfortable for general note-taking.

This is the model to choose if you want color variety. Whether you're color-coding notes, journaling, or doing any kind of artistic work that benefits from multiple hues, the standard one gives you the most options. The limited edition colors are also usually released in this format first, like the Fika series with its seven muted Scandinavian-inspired tones, or the various seasonal collections.

The 0.38mm tip is what I reach for most often. It writes fine enough for dense note-taking but doesn't feel scratchy. The 0.5mm is noticeably smoother but takes slightly longer to dry. The 0.7mm is the smoothest but puts down enough ink that you'll want to be more careful about smearing.

The one F is an upgraded version with a barrel that's slightly thicker than the standard one, weighted toward the tip for better control and reduced hand strain. It measures 14cm long with an 11.1mm diameter barrel that tapers down to about 9mm at the grip, ending in a metal nose cone.

Unlike the standard one, the F has a barrel made entirely of plastic with no rubber grip section. Some people worry about slipping, but the pen is deliberately weighted toward the tip and the wider body makes it extra comfortable for long writing sessions, though some slipping can happen without a grippy texture.

The key advantage here is ergonomics. The slightly wider diameter encourages a more relaxed grip, and that forward weight distribution means you don't feel like you need to press hard to get the pen to write. If you're someone who writes for hours at a time or tends to grip pens too tightly, the F addresses those issues.

The trade-off is limited color options. The F only comes included with black ink refills in 0.38mm and 0.5mm sizes. You get interesting barrel colors in various limited editions (the Earth Texture series with speckled barrels, the Marriage Color series, etc.). Although of course, you can always swap in any other ink color from the uni-ball one UMR ink refills, which are compatible with all uni-ball one products.

I keep an F at my desk for longer writing sessions. The weight distribution really does make a difference when you're working through several pages of notes or correspondence.

The P stands for "Pocket," and this model features a shorter and broader body compared to the F, making it more convenient to carry around. At about four and a half inches in length, it's shorter than the average pen, but its chunky body balances out the compact size and makes it surprisingly comfortable to hold and write with.

The P has a stabilizer mechanism that provides stable writing with a low center of gravity. This is important because short pens can feel unstable or cramped. The P avoids this by being wider and having that low center of gravity design.

Like the F, the P has a barrel made entirely of plastic and only comes with black ink in 0.38mm or 0.5mm. It also uses the same refills as the standard one and one F.

This is the pen for portability. If you carry a small notebook in your pocket, if you want something that won't take up much space in a bag, or if you just prefer shorter pens, the P works well. I keep one in my jacket pocket for quick notes when I'm away from my desk. The chunky grip makes it perfectly usable despite the compact size.

The various limited edition P models lean into the cute aesthetic. There's the Flavor Jelly series with translucent frosted barrels, the Bath Bomb series, and others that embrace a more playful design language. If that appeals to you, the P has more personality than the other models.

Here's how I'd break down the decision:

Choose the standard one if you need color variety, if you're doing any kind of color-coding work, if you want the option of different tip sizes including 0.7mm, or if you prefer a lighter pen with a rubber grip.

Choose the one F if you write for extended periods, if you tend to grip pens too tightly and want something that encourages a lighter touch, if you primarily use black ink, or if you prefer a more professional appearance with the metal tip.

Choose the one P if portability matters, if you carry a small pocket notebook, if you prefer shorter pens, or if you want something with a bit more design personality through the limited edition color options.

All three share the same core ink technology, so you're getting that distinctive vibrant pigment formula regardless of which body style you choose. They're all retractable with the same spring-loaded clip that opens wide when you press near the push button, so you won't lose caps and you can easily clip them to notebook covers.

One thing to keep in mind: some users report that these pens run out of ink fairly quickly, so you may want to stock up on refills if you write frequently. The refills are readily available and not expensive, but it's something to factor into your planning.