I get this question all the time, and my short answer is yes: if you normally like a Western fine, you should usually look at a Japanese medium; if you like a Western medium, start with a Japanese broad. Japanese nibs are not universally tiny, but after testing more than 200 pens, the pattern is consistent enough that I treat it as the default unless a brand has a known exception.
The reason this trips people up is that “size up” sounds too simple for what is really a writing-system and tuning issue. Japanese brands often grind nibs for cleaner line control, tighter handwriting, and better behavior on thinner paper, so the same letter on the nib does not always produce the same ink footprint as a German or American pen. When I compare pens side by side on Rhodia and copy paper, I usually see Japanese nibs run about half to one size finer than their Western counterparts, which is enough to change how a pen feels, shades, and handles your everyday notebook.
The Short Answer
If you are buying a Japanese nib and you want the same line width you already enjoy from most Western brands, sizing up one step is the safest move. In plain terms, a Japanese fine often writes like a Western extra-fine or fine, and a Japanese medium often lands close to a Western fine or fine-medium. That is not a law of physics, but it is the best starting rule I use when advising people.
My practical verdict is this: size up when your priority is matching familiar line width, stay at the same size when you specifically want more precision, and do not size up blindly if you are shopping within specialty nibs like soft, music, zoom, or extra-fine grinds. I have had this play out repeatedly: a Sailor medium-fine felt perfect for small planner writing, but the same buyer expecting a Western medium would have called it too narrow within two pages.
| If you normally like… | Start here in a Japanese nib | Why |
|---|---|---|
| Western EF | Japanese EF or F | Depends on how smooth you want the pen to feel versus how narrow you want the line |
| Western F | Japanese M | Usually the closest all-around match for daily writing |
| Western M | Japanese B | Gives you a similar visual weight without feeling unexpectedly needle-like |
| Western B | Japanese B or specialty broad/stub | Standard Japanese broad can still look restrained compared with Western broad nibs |
What Is Probably Causing the Problem
When someone asks whether they should size up, the real problem is usually that they are using one label system to predict another. The nib stamp says F, M, or B, but that stamp is not a universal measurement. What matters is the actual tipping shape, ink flow, paper absorbency, and the brand’s design target.
- Japanese brands often tune nibs for finer, more controlled writing because smaller handwriting and lower-quality paper are common use cases.
- Western brands often leave more tipping and wetter flow, which makes the same labeled size put down a broader line.
- Paper changes the result more than most buyers expect; a fine nib on absorbent office paper can look broader than it does on coated stationery.
- Some brands have their own internal scale, so Pilot, Sailor, and Platinum do not line up perfectly with each other even before you compare them to Lamy, Pelikan, or JoWo-made nibs.
That is why people end up disappointed after buying “their usual medium” from a Japanese maker. The nib is not wrong; the expectation was. One of my recurring test notes is that Pilot’s gold medium is often the easiest crossover point for Western fine users, while Sailor’s medium-fine can feel much narrower than the label suggests if your baseline is a wetter European pen. If you want a quick way to compare what a nib is actually doing on paper, I like using a dependable pad such as Rhodia dotpad A5 because it reduces paper noise and shows the nib more honestly.
What I Check First
Before I tell anyone to exchange a pen or buy a different size, I check four things at the desk. This takes ten minutes and usually explains whether the nib is truly too fine or whether the writing setup is making it seem that way.
- Compare the pen on two papers: one fountain-pen-friendly sheet and one normal office sheet.
- Write a full paragraph, not just loops and lines, because real handwriting reveals spacing and comfort problems fast.
- Check ink flow with a known moderate ink instead of a very dry or very wet formula.
- Look at your normal writing size; if your handwriting is compact, the finer Japanese line may actually be helping you.
I also inspect the nib before blaming the size. A simple 10x jeweler’s loupe is one of the best cheap tools a pen owner can keep nearby. Under magnification I am looking for tine alignment, overly tight slit spacing, or baby’s bottom, because a misaligned or hard-starting nib can fool people into thinking they bought the wrong width. I have had pens that felt disappointingly sharp in Japanese fine, then became perfectly usable after a minor alignment check. If the line looks starved and pale, try a lubricated, middle-of-the-road ink such as Pilot Iroshizuku Take-sumi before deciding the nib is the problem.
How I Fix It Step by Step
If the nib genuinely feels finer than you want, I do not jump straight to grinding or replacing parts. I work through the least risky fixes first. Most of the time, the goal is not to force a Japanese fine to become a medium; it is to confirm whether sizing up on your next purchase is the smarter solution.
- Start with a controlled paper-and-ink test to separate nib width from paper spread and dry flow.
- Flush the pen thoroughly, then retest with a known well-behaved ink.
- If the nib feels scratchy or unusually stingy, inspect tine alignment and slit cleanliness before assuming the size label is the issue.
- If you still want a broader, more relaxed line after that, exchange or repurchase one size up rather than aggressively modifying the nib.
Here is the exact process I use at home.
- Write a baseline sample. Use your normal pressure and write one paragraph on decent paper and one paragraph on cheap paper. If the nib looks fine on Rhodia but broad enough on copier paper, you may already have the right size for real-world use.
- Flush the pen. Manufacturing oils, dried ink residue, or converter contamination can make a new nib write drier and narrower than it should. Plain water is enough for most pens. Let it dry briefly, then ink again.
- Standardize the ink. Dry inks exaggerate the “too fine” feeling. A wetter, better-lubricated ink can make a Japanese medium feel more substantial without touching the nib. This is the fastest non-destructive fix I know.
- Check tine alignment. Under a loupe, the tips should meet evenly. If one tine sits higher, the pen may feel sharper and deliver inconsistent flow. Minor alignment issues are common and can distort your impression of line width.
- Use brass shims only if flow seems restricted. A thin fountain pen brass shim can help clear debris from the slit, but this is a cleaning step, not a widening tool. I do not recommend forcing the tines apart unless you are comfortable accepting damage risk.
- Decide whether the mismatch is functional or emotional. If the pen writes well but simply looks narrower than your Western favorite, the honest fix is usually to buy the next size up. If you want broad shading, looser signatures, or a softer visual line, sizing up is the correct move.
My strongest verdict here is simple: do not buy a Japanese fine and plan to “tune it into” a Western medium later. That is usually bad economics and worse nib care. A nibmeister can broaden a nib to a degree, but you are paying extra to solve a sizing decision that should have been made at checkout. For most buyers, the cleanest fix is to exchange the nib size early, keep a small comparison notebook, and use consistent test paper so your future choices are faster and more accurate.
When It Needs Professional Repair
If the pen is not just finer than expected but also scratchy, hard-starting, skipping, or visibly misaligned, you may be dealing with a nib problem rather than a sizing issue. That is when I stop treating it as a buying decision and start treating it as a repair question. A good nibmeister can correct tine alignment, improve flow, smooth the tipping, and tell you whether the nib geometry is normal for that model.
I would hand the pen off if the tines are bent, the slit is obviously uneven, the tipping looks malformed, or any home adjustment starts to feel forceful. Gold and steel nibs are more durable than beginners think, but they are also easy to overcorrect. If the pen is expensive, limited, or sentimental, professional help is cheaper than replacing a damaged nib. The key distinction is this: if the pen writes properly and just feels too fine, size choice is the issue; if it writes poorly, repair comes first.
Bottom Line
Yes, you should usually size up when buying a Japanese nib if your goal is to match the line width you know from Western pens. The rule is not perfect, but it is reliable enough that I use it as the default recommendation: Western fine buyers should look hard at Japanese medium, and Western medium buyers should usually start at Japanese broad.
The smarter way to approach this is not to memorize brand mythology but to diagnose your real use case. If you write small notes on ordinary paper, the finer Japanese grind may be exactly why the pen works. If you want the same visual weight, smoothness, and ink presence you get from a Western nib, size up early and save yourself the repair bench detour. That is the engineer’s answer here: treat nib labels as starting points, test on actual paper, and make the least destructive fix that solves the problem.