Chemex Filter Sizes: Which Ones Actually Fit Your Carafe?
Chemex sells four filter shapes under codes nobody explains, and the small-carafe filters do not fit the big carafe. Here is which box to buy for the Chemex you own.
Tomas Reyes
August 28, 2026
5 min
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Chemex filters are the most confusing consumable in coffee, and it is entirely an labeling problem. The filters are sold under product codes — FP-1, FC-100, FP-2, FSU-100 — that describe the fold and the shape but bury the one thing you need to know, which is whether the filter fits the carafe sitting on your counter. Buy wrong and you get one of two failures: a filter too small that collapses into the cone and lets grounds through, or a filter too large that bunches against the glass, seals the air channel and stalls the drawdown halfway.
The good news is that the entire system reduces to a single split. Chemex makes exactly two filter sizes. Everything else is a choice of shape and folding convenience.
The only split that matters: small carafe or large carafe
- 3-cup carafe (and the small handblown models): takes the SMALL filters — sold as FP-2 (pre-folded half-moon) or the small circles. Roughly 4.5 in / 11.5 cm folded.
- 6-cup, 8-cup and 10-cup carafes: all take the SAME LARGE filter — FP-1 (pre-folded squares), FC-100 (circles), FSU-100 (unfolded squares). Roughly 6.5 in / 16.5 cm folded.
- Squares vs circles: identical brewing. Squares fold to a cone with a thicker three-layer side; circles do the same with less bulk. Pure preference.
- Pre-folded vs unfolded: unfolded is cheaper per filter and folds in about four seconds. Pre-folded is the convenience tax.
Read that list again, because it contains the fact that saves most people a wasted order: the 6, 8 and 10-cup Chemex carafes all use the same filter. The carafe gets taller, the cone at the top does not get wider. Only the 3-cup is different. If you own anything other than the little one, buy the large filters and stop thinking about it.
Why the thickness is the point (and why generic filters disappoint)
Chemex paper is 20–30% heavier than standard pour-over paper. That is the whole design: it traps more oils and fine particles, which is why a Chemex cup tastes noticeably cleaner and lighter-bodied than the same coffee through a V60. It is also why the brew is slower and why the fold matters — the three-layer side goes against the pouring spout, holding the air channel open so the carafe can breathe as it drains.
Substituting a thinner generic cone filter technically works and will not hurt anything, but you are then brewing a Chemex that tastes like a V60. If the clean cup is why you bought the thing, the paper is not the place to save four dollars.
Our picks, compared
Chemex 6-Cup Pour-Over Carafe
Slow weekend mornings and brewing for two.
Chemex 3-Cup Pour-Over Carafe
One person brewing one mug at a time and nothing larger.
So which box should you buy?
Own a 6, 8 or 10-cup: buy FP-1 pre-folded squares if you want to grab and go, FC-100 circles if you find the square's bulk annoying in the cone, or FSU-100 unfolded squares if you brew daily and want the lowest cost per cup. Own the 3-cup: you need FP-2, and you need to check the listing says 3-cup or small, because the big-carafe boxes look nearly identical in thumbnails.
Skip the math — use the coffee ratio calculator
Once the filter is right, the dose is the other half. Run your carafe size through the ratio calculator:
Open the calculator15 g
- Do the 6-cup, 8-cup and 10-cup Chemex use the same filters?
- Yes. The 6, 8 and 10-cup carafes all take the same large Chemex filter (FP-1 squares, FC-100 circles, or FSU-100 unfolded squares). The carafes differ in height and capacity, not in the width of the cone, so one box of large filters covers all three. Only the 3-cup carafe needs the smaller FP-2 filters.
- What is the difference between FP-1 and FC-100 Chemex filters?
- FP-1 are pre-folded squares and FC-100 are circles. Both are the large size, both are the same heavyweight bonded paper, and both brew identically. The square folds into a cone with slightly more bulk on the three-layer side; the circle sits a little flatter. Choose on feel, not on flavor.
- Can I use regular cone filters in a Chemex?
- They will physically work if the size is close, but Chemex paper is 20–30% thicker than standard pour-over paper, which is what produces the signature clean, oil-free cup. A thinner generic filter brews faster and tastes closer to a V60. It is safe, just not what you bought a Chemex for.
- Which side of a folded Chemex filter goes against the spout?
- The thick three-layer side. It braces the paper against the pouring spout and keeps an air channel open so the carafe can vent while it drains. Put the single-layer side there and the filter tends to seal against the glass and stall the drawdown.
Tomas Reyes
Tomas is a coffee equipment reviewer and former Q-grader. He has tested over 200 home grinders in the last eight years and writes a quarterly buyer's guide.