Fountain Pen Converters: A Complete Guide
By Claire Ashford . 8 min read . Updated June 2026
A converter is the upgrade that opens the full bottled ink market to a cartridge pen. Instead of buying manufacturer-specific cartridges in a limited color range, you fill from any of the thousands of bottled inks available from brands like Pilot, Diamine, J. Herbin, or Robert Oster. The converter costs less than five refills of proprietary cartridges and pays for itself within months for any regular writer. This guide covers the right converter for the most popular pen brands, how to fill without mess, and when an eyedropper conversion makes more sense than any converter.
The short answer
A fountain pen converter replaces a disposable cartridge to let you fill the pen from any bottled ink. Converters are brand-specific: Pilot, Lamy, Platinum, and Sailor all use proprietary sizes. The Pilot CON-70+ is the highest-capacity standard converter. For maximum ink capacity in a cartridge pen, eyedropper conversion of a compatible plastic pen holds more than any converter.
This guide contains affiliate links. NibPath may earn a commission at no cost to you.
Converter compatibility by pen brand
Converters are not universal. Each pen brand uses a proprietary size and locking mechanism. Buying the wrong converter means a loose, leaking fit that defeats the purpose of using one. The major brand fits are straightforward once you know them.
For Pilot pens including the Metropolitan, Kakuno, Prera, Custom 74, and Explorer: use the Pilot CON-70+ Ink Converter . It holds approximately 1.1ml and fits the full range of Pilot cartridge-compatible pens. The older CON-40 holds less and is a reasonable budget option, but the CON-70+ is worth the slight price difference for the added capacity.
For Lamy pens including the Safari, Al-Star, Studio, Joy, and CP1: use the Lamy Z28 Ink Converter . It is the only converter sized for the Lamy fill section and is readily available from any Lamy retailer. For Platinum pens including the Preppy, Plaisir, Cool, and Century: use the Platinum Converter 700S .
European standard converters (used by TWSBI in some models, Kaweco, and many other brands) share a common size but vary by pen slot length. Always confirm that a European standard converter fits the slot depth in your specific pen before buying.
Pilot CON-70+ Ink Converter
The highest-capacity standard converter from Pilot, holding approximately 1.1ml of ink. Fits all Pilot cartridge-compatible pens including the Metropolitan, Kakuno, Prera, Custom 74, and Explorer. The plus version uses a push-knob fill mechanism.
Lamy Z28 Ink Converter
The standard piston converter for Lamy pens with the Lamy cartridge-converter fill section, including the Safari, Al-Star, Studio, and Joy. Holds approximately 0.8ml, transparent, and widely available from any Lamy retailer.
Platinum Converter 700S
A piston converter for Platinum fountain pens including the Preppy, Plaisir, Cool, Century, and Izumo. The Platinum proprietary converter section fits no other brand but holds approximately 0.8ml and seals reliably.
How to fill a converter without making a mess
Fill with the pen assembled and the converter seated in the grip section. Open your ink bottle and submerge the nib fully below the ink surface, not just the tip. If you only submerge the tip, the feed does not prime properly and you get an air bubble instead of a full converter.
For a piston converter ( Pilot CON-70+ Ink Converter , Lamy Z28 Ink Converter ): twist the knob back fully to expand the chamber before submerging. Once the nib is fully submerged, slowly twist the knob forward to draw ink. Fill slowly rather than twisting in one motion to prevent air bubbles.
For a squeeze converter: depress the reservoir fully before submerging the nib, then release slowly once submerged. The release draws ink up through the feed.
Wipe the nib and grip section with a paper towel before capping. A blunt-tip syringe is the cleanest alternative for filling narrow converter openings or for transferring ink samples into the converter without submerging the full nib assembly.
Pilot CON-70+ Ink Converter
The highest-capacity standard converter from Pilot, holding approximately 1.1ml of ink. Fits all Pilot cartridge-compatible pens including the Metropolitan, Kakuno, Prera, Custom 74, and Explorer. The plus version uses a push-knob fill mechanism.
Noodler's Blunt Tip Ink Syringe Set
A set of blunt-tipped dispensing syringes for precise ink filling, sample transfers, and eyedropper conversions. The 1ml and 3ml sizes cover most fountain pen tasks. Compatible with all fountain pen inks.
Eyedropper conversion: maximum capacity for compatible pens
An eyedropper conversion turns the entire pen barrel into the ink reservoir, bypassing the converter entirely. The Kaweco Sport Eyedropper Conversion Kit specifically sizes the O-ring and silicone grease for the Kaweco Sport's grip-barrel threads, which is the most common eyedropper conversion. The converted Sport holds approximately 1.4ml compared to a converter's 0.7ml to 1.1ml.
The conversion works only on pens with an all-plastic barrel and a threaded, removable grip section. The silicone grease seals the barrel threads to prevent leakage. Apply a thin, even layer to all threads before filling and test over a paper towel before pocketing the converted pen.
The tradeoff for eyedropper capacity is that you cannot quickly switch ink colors without emptying and cleaning the entire barrel. It is the right choice for a pen you plan to use with one ink for extended periods, not for a pen you switch frequently.
Kaweco Sport Eyedropper Conversion Kit
A silicone grease and O-ring kit specifically sized for the Kaweco Sport's grip-barrel thread. Converts the plastic Sport to an eyedropper pen holding approximately 1.4ml of ink. Straightforward to apply and reverse.
When to move beyond converters entirely
If you find yourself refilling a converter pen every day or two, it is a signal that a dedicated piston-filling pen like the TWSBI ECO Demonstrator Piston Filler makes more sense. The ECO's 1.9ml piston reservoir holds nearly double the Pilot CON-70+ Ink Converter 's capacity and the ink level is visible through the demonstrator body at all times.
Piston pens also eliminate the slight inconsistency of converter fill positions, which can vary between fills and affect ink flow. A well-maintained piston pen fills to the same level every time. The TWSBI ECO Demonstrator Piston Filler is the standard recommendation for a first piston-fill pen and costs within reach of most writers who are ready to commit to the upgrade.
TWSBI ECO Demonstrator Piston Filler
Not a converter but a complete piston-filling pen with a visible ink reservoir of approximately 1.9ml. Listed here because writers often move to a piston pen to eliminate converter limitations. The ECO is the most recommended entry-level piston filler.
Featured in this guide
Pilot CON-70+ Ink Converter
The highest-capacity standard converter from Pilot, holding approximately 1.1ml of ink. Fits all Pilot cartridge-compatible pens including the Metropolitan, Kakuno, Prera, Custom 74, and Explorer. The plus version uses a push-knob fill mechanism.
Lamy Z28 Ink Converter
The standard piston converter for Lamy pens with the Lamy cartridge-converter fill section, including the Safari, Al-Star, Studio, and Joy. Holds approximately 0.8ml, transparent, and widely available from any Lamy retailer.
Platinum Converter 700S
A piston converter for Platinum fountain pens including the Preppy, Plaisir, Cool, Century, and Izumo. The Platinum proprietary converter section fits no other brand but holds approximately 0.8ml and seals reliably.
Kaweco Sport Eyedropper Conversion Kit
A silicone grease and O-ring kit specifically sized for the Kaweco Sport's grip-barrel thread. Converts the plastic Sport to an eyedropper pen holding approximately 1.4ml of ink. Straightforward to apply and reverse.
TWSBI ECO Demonstrator Piston Filler
Not a converter but a complete piston-filling pen with a visible ink reservoir of approximately 1.9ml. Listed here because writers often move to a piston pen to eliminate converter limitations. The ECO is the most recommended entry-level piston filler.
Noodler's Blunt Tip Ink Syringe Set
A set of blunt-tipped dispensing syringes for precise ink filling, sample transfers, and eyedropper conversions. The 1ml and 3ml sizes cover most fountain pen tasks. Compatible with all fountain pen inks.
Keep reading
Related roundups
FAQ
Frequently asked questions
Do converters fit all ink bottles?+
Converters work with any bottled ink regardless of the bottle design. You submerge the pen's nib in the ink rather than inserting a nozzle into the bottle. Wide-mouth bottles like many Pilot Iroshizuku bottles allow easy full nib submersion. Narrow bottles may require a blunt-tip syringe to transfer ink to a wider container before filling.
Why is my converter leaking?+
The most common causes are an overfilled converter (ink expands slightly with temperature changes), a converter that is not fully seated in the pen's fill section, and a worn or cracked converter that no longer holds pressure. Try underfilling the converter by about a quarter of its capacity when carrying in warm conditions, and verify the converter seats firmly without wobble before capping.
How long does a converter last?+
A quality piston converter lasts years with routine cleaning. The piston seal may harden slightly over time and benefit from a drop of silicone grease on the piston. Replace the converter when the piston becomes stiff enough to affect filling or when the body cracks and begins leaking regardless of seal treatment.