Cold Brew Calculator

Concentrate vs ready-to-drink — pick your workflow

Cold brew comes in two practical formats, and the ratio you choose decides which one you get. A concentrate, brewed around 1:5 (one part coffee to five parts water by weight), is deliberately over-strong — you're never meant to drink it straight. The payoff is flexibility and shelf life: a jar of concentrate keeps in the fridge for one to two weeks, takes up a fraction of the space a diluted batch would, and lets everyone in the house cut it to their own taste on the spot — strong over ice, gentle with milk, somewhere in between. This is why nearly every café that serves cold brew off a tap is pouring from a concentrate, not a ready-to-drink batch; a five-gallon keg of concentrate serves far more customers than the same keg brewed weak enough to sip directly.

A ready-to-drink batch, brewed looser around 1:8, is the opposite trade: less flexible, but zero extra steps. Pour it over ice and drink it — no measuring, no math, no risk of a badly-judged dilution ruining the glass. It's the better choice when you know exactly how you like your cold brew and don't want a concentrate jar taking up fridge space between servings, or when you're serving a crowd who'll pour their own glass without a ratio card in hand. Use the Style control above to switch between the two, or drag the ratio slider to anywhere in between — 1:6 and 1:7 are common middle-ground choices for people who want less math at serving time without going all the way to a full ready-to-drink strength.

The 2.2× rule: why your jar yields less than you think

Every cold brew recipe you'll find online states the water you pour IN. Almost none of them tell you how much beverage you actually get OUT, and the gap between those two numbers is bigger than most people expect. Immersion brewing — grounds fully submerged for hours, as opposed to water draining through them in a pour-over — traps roughly 2.2 grams of water per gram of dry coffee. That water doesn't evaporate or disappear; it's just retained inside the swollen grounds when you lift the sock out, the same way a sponge holds water after you dunk it.

Run the numbers on the calculator's default: a 1 liter jar at 1:5 uses 200 g of coffee. That 200 g of grounds retains 2.2 × 200 = 440 ml of the water you poured in — leaving 1,000 − 440 = 560 ml, not 1,000 ml, as your actual yield. Plan a party around "I poured a liter, that's about four 250 ml glasses" and you'll come up short by more than a full glass. The fix is to plan backwards: decide how many glasses you actually want, multiply by your serving size, and let the calculator's batch inputs solve for the container that delivers it — rather than guessing a container size and hoping the yield works out.

Steep time & temperature

Cold extraction is slow by design — that's the entire point of the method. Cold water dissolves coffee's soluble compounds far less readily than hot water does, so instead of finishing in minutes the way a pour-over does, cold brew needs hours of contact time to pull out a comparable amount of flavor. Room-temperature ("counter") steeping runs faster because warmer water always extracts more readily than cold, landing in a 12-16 hour window with 14 hours the sweet spot for most ratios. Fridge steeping is slower — the near-freezing temperature drags extraction out further, needing 16-24 hours with 20 hours as the sweet spot — but the tradeoff is a wider safety margin: a batch that's "ready" at 18 hours in the fridge still tastes good at 22, where a counter batch moves out of its good window faster.

The over-steep myth worth retiring: extraction doesn't have an "off switch." Past roughly 24 hours, you're not getting a stronger cup, you're pulling material that was never worth extracting in the first place — woody, dusty, flat notes that dilution can't fix because they dilute right along with everything else. If a batch has gone past its window, the fix for next time is a shorter steep, not a bigger dilution on this one.

Grind size for cold brew

Go coarse — coarser than drip, closer to the texture of raw sugar or coarse sea salt. Cold brew's long contact time is forgiving of a coarse grind (the hours make up for the reduced surface area), but it's unforgiving of a fine one: fine particles ("fines") suspended in cold water for 12-24 hours don't just over-extract, they physically pass through most filters and settle at the bottom of your cup as silt. A cafetière-coarse or coarser setting keeps the bed loose enough to filter cleanly and keeps the extraction from running away into bitterness over such a long steep. For a deeper breakdown of exactly how coarse to go and why particle size matters more here than in almost any other method, see our full guide to cold brew grind sizes.

Dilution playbook

Once you've got a concentrate, dilution is where the actual drink gets made. Water gives you the cleanest read on the coffee itself — nothing masking the flavor, so it's the fairest way to judge a new bean or a new batch. Milk rounds out acidity and adds body, the classic cold-brew-latte move, especially with concentrate ratios on the stronger end (1:4-1:5) so the coffee doesn't get lost. Oat milk splits the difference — it adds some of milk's body and sweetness without milk's full dairy weight, and its slightly nutty, faintly sweet profile tends to complement chocolatey and nutty roasts particularly well.

The "drinks like" number above (effective ratio = R × (1 + dilution)) tells you where your final glass actually lands on the strength scale — a 1:5 concentrate cut 1:1 drinks like a 1:10, which sits comfortably inside the familiar 1:15-1:17 range you'd use for hot filter coffee once you account for ice. That's the other half of the picture: ice isn't neutral. As it melts it adds roughly another 20-25% dilution on top of whatever you poured, meaning a glass that reads 1:10 fresh out of the shaker can finish closer to 1:12-1:13 by the time you've worked through the ice. If you like your cold brew strong all the way to the bottom of the glass, dilute slightly less than you think you need and let the ice finish the job.

Cold brew vs iced coffee vs flash brew

These three get used interchangeably in casual conversation, but they're genuinely different drinks, brewed in different ways, with different flavor profiles and different caffeine loads per ounce:

If low acidity and a smooth, mellow, chocolatey cup is what you're after, cold brew is the method built for it. If you want the bright, aromatic character of a hot pour-over served cold without the flatness that comes from simply chilling a hot brew, flash brewing is the better fit — brew hot directly onto ice so the aromatics get locked in by the instant temperature drop instead of fading as the coffee slowly cools. Our Japanese iced coffee calculator runs that exact method: exact ice, hot water and coffee for a flash-brewed glass, plus the predicted serving temperature.

Which beans?

Cold extraction is a flattening process — it mutes the bright, acidic, fruit-forward notes that make a light-roast washed Ethiopian sing hot, and amplifies body and sweetness instead. That makes chocolatey, nutty, low-acid singles and blends the natural fit: Brazilian and other South American beans with cocoa and nut-forward tasting notes tend to shine in cold brew specifically because those are the characteristics cold extraction preserves and even emphasizes, while the acidity that would otherwise compete for attention gets dialed down. A washed, high-acidity light roast isn't a bad choice, but expect it to taste noticeably rounder and less bright cold-brewed than it does through a hot pour-over — if that bright acidity is the whole reason you love the bean, cold brew may undersell it.