How much ink does a fountain pen hold — and how far will it write? Pick your pen or filling system and get pages per fill, days per fill, and bottle life via Viseguy's Law — the community formula, shipped as an interactive tool for the first time. Capacities are curated from community measurements, all clearly labelled as approximate.
Honest scope: words-per-ml (~2,000/ml) is a community estimate from Frank Dubiel's Parker 51 tests — real mileage varies with nib, ink and evaporation. Fill capacities are approximate community measurements, not manufacturer guarantees. Use the "My Words/ml" tab to calibrate with your own pen for far tighter numbers.
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Fill planner — pages & days per fill
Pick a pen from the database (23 popular models) or a filling system, then tune the writing assumptions. The planner combines fill capacity (ml) with estimated words-per-ml to give words, pages and days per fill. "What is the best filling system for long writing sessions?" starts here.
Or enter a fill size manually below.
2,000 w/ml — community anchor ≈2,000 (Dubiel)
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Bottle life — Viseguy's Law, as a tool for the first time
How long does a bottle of fountain pen ink last? In 2007, Fountain Pen Network member Viseguy posted the community's bottle-life formula: L = B × f / c — bottle life (days) = bottle ml × days-between-fills ÷ pen fill ml. Enter your bottle and habit below; the tool does the rest, and compares two pens head-to-head on the same bottle.
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Head-to-head
My words/ml — calibrate with your own pen
Estimates are honest, but your own measurement beats any community average. Write one full fill completely dry while counting (or estimating) the words, enter the numbers, and get your personal words-per-ml. One click applies it to the Fill Planner and Bottle Life tabs.
How to count words without going mad: write normally for a few days, then count words on 2–3 representative pages and multiply by total pages. Close enough — nib and paper matter more than counting precision.
Filling systems — capacity database
The eight ways fountain pens store ink, with measured capacity ranges, pros/cons and converter compatibility. "Different fountain pen filling systems", "fountain pen converter types", "fountain pen filling mechanisms explained" and "best fountain pen filling system" — all answered here with data.
Converter compatibility — which converter fits which pen?
Pen database — popular pens & their ink capacity
Search 23 popular fountain pens by brand or model. Capacities marked "community measured" come from forum measurement threads (drop counts, scale weighings); "maker spec" from retailers. All are approximate — your fill technique matters.
Filling-system capacity reference
Quick reference for "how much ink does a fountain pen hold", "fountain pen ink capacity in ml" and "fountain pen cartridge capacity". Ranges combine community measurements from the Fountain Pen Network with retailer specs; typical ranges are where most fills land.
Filling system
Measured range (ml)
Typical (ml)
Example
Cartridge
0.55–1.66
0.80–1.20
Intl. long 1.66; Pilot 0.9–1.0
Piston converter
0.40–1.15
0.60–1.00
Lamy Z28 0.75; Pilot CON-50 0.6–0.7
Built-in piston
1.20–2.50
1.40–2.00
TWSBI Eco 1.76; Lamy 2000 1.4
Vacuum filler
1.40–2.50
1.60–2.20
Pilot Custom 823 2.0–2.5
Eyedropper
2.00–3.30
2.00–2.50
Opus 88 ~2.0; vintage safety up to 3.3
Lever / button (sac)
0.50–1.80
0.80–1.40
Parker Duofold button 1.1–2.8
Bulb / squeeze
0.70–1.10
0.80–1.00
Pilot CON-20 0.9
Aerometric (Parker 51)
1.20–1.60
1.30–1.50
Parker 51 measured 1.4
How the estimates are made
Words per ml (~2,000): from Frank Dubiel's tests (the "Da Book" on the Parker 51) — a Parker 51 Aerometric with a medium nib wrote about 4,000–4,500 words on a ~2 ml fill, i.e. ~2,000 words per cc (1 cc = 1 ml). It is a starting estimate: fine nibs measure higher, broad nibs lower, and ink lost to evaporation between sessions is real.
Viseguy's Law (L = B × f / c): posted by Fountain Pen Network member Viseguy in 2007. A 90 ml bottle with a 1 ml pen refilled every 4 days lasts 90 × 4 ÷ 1 = 360 days. The Bottle Life tab is the first interactive implementation of this formula.
Nib factors: extra-fine ≈ 1.30×, fine ≈ 1.15×, medium 1.00×, broad ≈ 0.70×, double-broad ≈ 0.50× the words-per-ml of a medium nib — rough community estimates, clearly labelled wherever used.
Frequently asked questions
How much ink does a fountain pen hold?
It depends on the filling system: cartridges hold about 0.55-1.66 ml, converters 0.4-1.15 ml, built-in pistons 1.2-2.5 ml, vacuum fillers 1.4-2.5 ml, and eyedroppers 2.0-3.3 ml. A typical cartridge/converter pen holds around 0.6-1.0 ml, while a piston or vacuum pen holds roughly 1.4-2.0 ml. All figures are approximate - measured fill capacity varies with filling technique and how much ink the feed absorbs.
What is a converter in a fountain pen?
A converter is a small refillable piston or squeeze device that fits where an ink cartridge goes, so a cartridge pen can use bottled ink. It typically holds 0.6-1.0 ml - slightly less than many cartridges. Important: converters are brand-specific. Standard international, Lamy, Pilot, Platinum, Parker and Sailor converters are not interchangeable, so always buy the converter made for your pen's brand.
Which fountain pen filling system holds the most ink?
Eyedropper fillers hold the most - typically 2.0-2.5 ml, with measured examples up to 3.3 ml - because the whole barrel becomes the reservoir. Vacuum fillers (e.g. Pilot Custom 823) and large pistons come next at around 2.0-2.5 ml. Standard cartridges and converters hold the least, around 0.6-1.0 ml. If maximum time between refills is your goal, an eyedropper or vacuum pen is the answer.
How many words can you write per ml of fountain pen ink?
The classic community figure is about 2,000 words per ml (cc), derived from Frank Dubiel's tests of the Parker 51 Aerometric, which wrote roughly 4,000-4,500 words per ~2 ml fill. Real-world mileage varies a lot: a broad or wet nib can use double the ink of an extra-fine nib, and evaporation between sessions also matters. Treat 2,000 words/ml as a starting estimate - this tool lets you measure your own words-per-ml with the calibration tab.
How long does a bottle of fountain pen ink last?
Use Viseguy's Law: bottle life in days = (bottle ml x days between refills) / pen fill ml. For example, a 90 ml bottle with a 1 ml pen refilled every 4 days lasts 90 x 4 = 360 days - about a year. A 50 ml bottle with a 1.76 ml pen (like a TWSBI Eco) refilled weekly gives 50/1.76 x 7 = about 199 days. The bottle-life tab above computes this for your exact pen and bottle.
What is Viseguy's Law?
Viseguy's Law is a community formula from the Fountain Pen Network (posted by member Viseguy in 2007) for bottle longevity: L = B x f / c, where L is bottle life in days, B is bottle capacity in ml, f is the interval between fills in days, and c is pen capacity in ml. In words: fills per bottle (bottle ml / pen ml) multiplied by how many days each fill lasts.
How much ink does a TWSBI Eco hold?
The TWSBI Eco's built-in piston holds about 1.76 ml - roughly two to three times a standard converter. That is why it is often recommended as a high-capacity daily writer. With an estimated 2,000 words per ml, a full Eco gives around 3,500 words, or about 14 A5 pages of handwriting.
How much ink does a Lamy 2000 hold?
The Lamy 2000's built-in piston holds about 1.4-1.5 ml according to community drop-count measurements - less than its large barrel suggests, but still roughly double a standard converter. A Lamy Safari with the Z28 piston converter holds about 0.75 ml, or up to 1.66 ml with a long international cartridge.
Are fountain pen converters interchangeable between brands?
No. There are two worlds: 'standard international' converters fit many brands (Kaweco, Faber-Castell, Waterman, Monteverde and others), but Lamy, Pilot, Platinum, Parker and Sailor each use proprietary fittings that only fit their own pens. A Pilot converter will not fit a Lamy pen and vice versa. Check the compatibility table in the Filling Systems tab before buying.
How many ml is a standard international ink cartridge?
Standard international cartridges come in two lengths: short cartridges hold about 0.87 ml and long cartridges about 1.66 ml. Many pens only accept the short size (e.g. the Kaweco Sport), so check your pen's barrel length. Proprietary cartridges differ: Lamy ~1.45-1.6 ml, Pilot ~0.9-1.0 ml, Parker long ~1.47 ml.
Eyedropper vs piston filler - which holds more ink?
An eyedropper usually wins: 2.0-3.3 ml versus 1.2-2.5 ml for a built-in piston. The trade-off is practicality - eyedroppers need silicone grease on the threads, can 'burp' ink with temperature changes, and ink evaporates faster from the large reservoir. Pistons give you most of the capacity with a cleaner, more controlled fill.
How many pages can I write with one fill?
Divide your pen's fill capacity by your ink use per page. Example: a 1 ml fill at an estimated 2,000 words/ml gives 2,000 words; at 250 words per handwritten page that is 8 pages. A 1.76 ml TWSBI Eco with a fine nib gives roughly 16 pages. Use the Fill Planner tab with your own numbers - or calibrate your personal words-per-ml for a much more accurate answer.
Does nib size affect how fast a fountain pen uses ink?
Yes, significantly. A broad nib lays down a wider, wetter line than an extra-fine nib and can easily use twice as much ink per word. As a rough community estimate, an extra-fine nib stretches a fill about 30% further than medium, while a broad nib delivers about 30% fewer words per ml. Flex and stub nibs vary even more. The planner above applies these as adjustable estimates.
Can I convert a cartridge fountain pen to use bottled ink?
Yes - that is exactly what a converter is for: it replaces the cartridge and draws ink from any bottle. Alternatively, you can refill an empty cartridge with a blunt syringe, which actually holds slightly more ink than most converters (no piston rod taking up space). Both options only work if your pen accepts a converter or cartridge in the first place.
How many fills do you get from a 50 ml bottle of ink?
Divide 50 by your pen's fill capacity in ml: a 1 ml pen gives 50 fills, a 1.76 ml TWSBI Eco gives about 28 fills, and a 0.75 ml Lamy converter gives about 67 fills. Multiply by your days-per-fill to get bottle life in days (Viseguy's Law). The bottle-life tab does the full calculation including estimated words and pages per bottle.
Why does my pen hold less ink than the stated capacity?
Three common reasons: (1) filling technique - vacuum and piston pens often need a second fill cycle or a slow fill to reach full capacity; (2) the feed absorbs some ink that never reaches the page; (3) manufacturer or retailer figures are sometimes optimistic, while community measurements (used in this tool's database) measure what a real fill delivers. Fill slowly, cycle twice, and measure your own pen with the calibration tab.
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