I've been using Pilot fountain pens as daily writers since 2021. In that time, I've made just about every mistake possible with both the CON-40 converter and Pilot cartridges. I bought the wrong converter — the old CON-50, which doesn't fit newer Pilot pens. I ruined a perfectly good shirt during a cleaning mishap. I once ordered 60 cartridges I didn't actually need, just to hit free shipping.
If you're weighing the CON-40 vs. Pilot pen cartridges, here's what I actually learned, including the math I should have done before spending money on both.
Why This Decision Matters
Pilot pens are excellent, but they're also a system. The CON-40 is currently the only converter that fits many modern Pilot models, including the Custom 74, the Custom Heritage 92, and the Falcon. Pilot cartridges are proprietary, which means you're locked into Pilot's ink if you go that route.
Both options work — they just work differently. To compare them fairly, I tracked four things over the past year: cost, ink capacity, ease of use, and ink selection. Not from a specs sheet, but from daily use on my desk.
The Cost Breakdown: Buy vs Rent Math
Here's something most reviews skip: the converter vs. cartridge question is a version of the buy vs rent calculator problem. With the CON-40, you pay one cost upfront, then buy bottled ink as needed. With cartridges, you pay a smaller amount each time. The per-purchase price is low, but the annual total is what matters — and the only way to know it is to track it.
I did. Here are my real numbers from the past 12 months.
CON-40: Converter cost $9.50 (purchased January 2024 from an online fountain pen retailer — the typical range is $8-12). A 50ml bottle of Pilot Iroshizuku ink runs about $28 and lasts me roughly four to five months of daily writing at about two pages per day. Annualized: around $70-75 including a replacement converter, assuming one fails.
Cartridges: A box of 12 Pilot cartridges goes for $3.50-4.50 from most retailers (publicly listed prices, January 2025; verify current rates). One cartridge lasts me about two to three days. Annualized: $50-60.
Yeah. Cartridges came out cheaper in my tracking.
That surprised me. I assumed the big bottle was the more economical route. Turns out, the cheap cartridges are genuinely cheap. But here's where I have to draw a boundary: I'm not a financial analyst, so I can't speak to optimizing this further. What I can tell you from a practical standpoint is that the difference is small enough that it shouldn't be your deciding factor.
Capacity: The Number That Annoyed Me
Here's a spec that changed my entire view: the CON-40 holds roughly 0.5ml of ink. The older CON-50 — the one Pilot discontinued and that doesn't fit many newer pens anyway — held about 1.1ml. A Pilot cartridge holds about 1.0ml.
In practice, that means the CON-40 gives you about half the ink per fill that a cartridge gives you. For a heavy writer, that's a daily refill. For me, it was a surprise delivered in the form of a pen that ran dry in the middle of a meeting.
At first I assumed my converter was defective. I ordered a replacement. Same result. That's when I learned this is just how the CON-40 is designed: a small reservoir combined with a slow, multi-turn piston mechanism. It works, but it demands patience.
The practical difference: with the CON-40, you get a smaller tank but you can top it off from a bottle anywhere. With a cartridge, you get a bigger reservoir but you're stuck until it's empty. If you write more than a few pages daily, you'll feel this difference quickly.
Filling: The Ritual vs. The Click
In September 2022, I loaded my CON-40 with a fresh bottle of Kon-peki. I twisted the piston several slow turns and watched the chamber fill. It looked full. I installed it, wrote a few lines — and got less than a page before it ran dry.
The problem, as I later discovered, is that the CON-40 doesn't draw a full fill on the first attempt. The recommended method is to fill, expel, and repeat three or four times. Nobody explains this in the package. It's the kind of thing you learn on a forum after your third failed attempt. (Note to self: I should honestly make a short video guide for new users; the text explanations are too abstract.)
Then there's cleaning. The converter's tiny parts trap ink, and rinsing it properly requires disassembly. I've ended up with ink-stained hands more times than I care to count. One time, during a particularly careless rinse at the office sink, I stained a light blue shirt. (Mental note: clean the converter right after emptying it, not after it dries out.)
Cartridges, by comparison, are a two-step process: push until it clicks, wait thirty seconds, write. No ritual. No mess. No learning curve. That simplicity is genuinely valuable, especially if you're in and out of meetings all day.
Ink Options: The One Clear Win
If you value variety, the CON-40 wins and it's not close.
Bottled ink gives you an enormous range: Pilot's Iroshizuku line alone has 48 colors, and brands like Diamine, Waterman, Sailor, and Herbin add hundreds more. I've tried maybe a dozen different inks in my Custom 74 with the CON-40. Only one gave me flow issues, and that was a quirky shimmer ink that's known to be high-maintenance.
Cartridges keep you within Pilot's lineup — which is excellent but limited to about eight standard colors. Blue, black, blue-black, and a few others. No shading inks. No shimmer. No seasonal limited editions.
But here's my honest confession: 90% of my daily writing is Pilot blue-black anyway. I bought three bottles of specialty ink in my first year, and two of them are still 80% full. The freedom mattered more to me in theory than in practice.
I'm not an ink chemist, so I can't speak to which inks perform best in which pens. What I can tell you from practical experience: if you're not the type to swap ink colors regularly, the cartridge lineup will probably cover your needs.
The Paper Clip Detour (It Applies, Trust Me)
Last year, I stocked the office supplies cabinet and chose standard paper clips over binder clips. At the moment of ordering, it seemed like the obvious pick. Then I needed to hold a 30-page contract together, and the standard clips failed immediately. They now sit in a drawer, essentially unused.
The mistake wasn't buying paper clips. It was buying the tool for an imagined use case instead of my actual one. My actual use case was thick stacks of paper. Binder clips solved that. Paper clips didn't.
I repeated the same pattern with pens. I bought the converter for the option of bottled ink — without ever checking how much bottled ink I would actually use. Once I ran the numbers, the decision became much easier.
Running the Real Numbers
You know those no-tax-on-overtime calculators, where you punch in your hours and rate to get an actual take-home figure? I started applying that same approach to pens: counting pages written per cartridge, page yield per bottle, and cost per actual page of writing.
- How many pages do I write daily?
- How long does a cartridge last me?
- How long does a converter fill last me?
- Which one do I reach for when I'm in a hurry?
Three of those four questions pointed toward cartridges for everyday use. The fourth — the long writing sessions — pointed toward the converter. The answer wasn't "one is better." The answer was "use each for what it's good at."
Which Should You Pick?
After four years and enough mistakes to fill a notebook, here's my honest take.
Choose cartridges if:
- You write for short bursts throughout the day
- You carry your pen in a pocket, bag, or desk drawer
- You don't want to manage ink bottles
- You're new to fountain pens and want zero fuss
Choose the CON-40 if:
- You write long sessions regularly — journaling, drafting, detailed notes
- You want access to the full range of bottled inks
- You don't mind the fill ritual or top off frequently
- You already own ink bottles
A friend who'd been using Pilot pens for years gave me the advice I should have taken earlier:
"Buy the converter, buy a box of cartridges, and let your habits tell you which one you actually reach for."
One suggestion I wish someone had given me in 2021: you don't have to choose one permanently. I keep a converter in my desk Custom 74 for focused writing sessions, and a box of cartridges in my bag for anything involving a commute. Both have their place. Both cost less than the $75 I spent on trial and error before settling into this routine.
There's something satisfying about finally having a setup that works. After the wasted ink, the stained shirt, and the half-filled converters, I know exactly which tool to reach for. That knowledge came from mistakes — but it doesn't have to. This article is the shortcut.