Cold brew coffee is made by steeping coarsely ground coffee in cold or room-temperature water for an extended period — usually 12 to 24 hours — rather than using hot water. The result is a smooth, low-acid concentrate or ready-to-drink brew that highlights the sweeter, chocolatey and fruity notes of the beans without the bitterness that high-heat extraction can introduce. Getting the coffee-to-water ratio right is the single most important variable in cold brew: too little coffee and the brew is thin and watery; too much and it is harsh and overpowering. This calculator handles the ratio maths, yield estimate, serving count and caffeine estimate all at once.
How it works
The core formula is straightforward:
Brew ratio = water (g) ÷ coffee grounds (g)
A result of 6 is written as 1:6 (one part coffee to six parts water). Higher numbers mean a weaker, more dilute brew; lower numbers mean a stronger, more concentrated one. The calculator then estimates the liquid yield you will actually recover after pressing or filtering the spent grounds, because those grounds absorb a significant volume of water during steeping. The absorption factor depends on grind size:
| Grind size | Absorption factor |
|---|---|
| Coarse (immersion/jar) | ~2.0 ml per gram of coffee |
| Medium (Toddy/bag) | ~1.7 ml per gram |
| Fine (cold drip) | ~1.5 ml per gram |
So if you use 100 g of coarse coffee with 500 g of water, the grounds absorb roughly 200 ml, leaving an estimated yield of ~300 ml. The caffeine estimate uses the widely cited figure of approximately 6 mg of caffeine per gram of arabica-equivalent grounds, multiplied by a cold-extraction efficiency factor of 70% (cold water extracts caffeine more slowly than boiling water):
Estimated caffeine (mg) = coffee (g) × 6 × 0.70 ≈ coffee (g) × 4.2
Worked example
You want a regular-strength cold brew for the week using a large mason jar:
- Coffee: 80 g, coarse-ground
- Water: 480 g (filtered)
- Ratio: 480 ÷ 80 = 1:6 — regular cold brew, ready to drink
Yield calculation:
- Absorption = 80 g × 2.0 = 160 ml absorbed by grounds
- Yield = 480 − 160 = 320 ml recovered after straining
- At 240 ml per serving: ~1.3 servings from this small batch
Caffeine calculation:
- Total caffeine = 80 × 4.2 = 336 mg in the whole batch
- Per serving = 336 ÷ 1.3 = ~258 mg per 240 ml cup
Scale to 200 g coffee / 1,200 g water (same 1:6 ratio) for a full-week batch of ~800 ml — about 3.3 standard cups.
| Coffee | Water | Ratio | Yield | Servings (240 ml) |
|---|---|---|---|---|
| 60 g | 480 g | 1:8 | ~360 ml | 1.5 |
| 80 g | 480 g | 1:6 | ~320 ml | 1.3 |
| 100 g | 400 g | 1:4 | ~300 ml conc. | 5 × 60 ml shots |
| 200 g | 1,200 g | 1:6 | ~800 ml | 3.3 |
Formula note
All calculations are pure arithmetic — no network calls are made. The absorption factors (1.5–2.0 ml/g) are practical averages derived from immersion and Toddy-style brewer testing; actual absorption varies by roast level (darker roasts are more porous), grind distribution and how firmly you press the grounds. The caffeine estimate carries ±20% uncertainty because bean variety, roast profile and specific grind surface area all affect extraction rate. Use it as a planning guide, not a precise medical measurement.