Cold Brew Ratios and Caffeine Yield: The Two-Stage Math

Cold brew is not iced coffee made differently — it is an extraction method governed by a ratio, and that ratio is lower than most people expect. Where hot pour-over runs at roughly 1:16 coffee-to-water, cold brew concentrate is commonly brewed anywhere from 1:5 to 1:8, then diluted before serving. Get that two-stage math wrong and you either waste beans or pour a cup that tastes like wet cardboard.

Cold Brew Ratios by Intended Use

Style	Coffee : Water (by weight)	Example for 1 L Water	Serve
Ready-to-drink	1 : 12	83 g coffee	Straight, over ice
Medium concentrate	1 : 8	125 g coffee	Dilute 1:1
Strong concentrate	1 : 5	200 g coffee	Dilute 1:2 to 1:3
Nitro / milk drinks	1 : 4	250 g coffee	Cut with milk or water

Weigh the coffee; do not scoop it. A level tablespoon of coarse coffee holds about 5 g, but the same spoon can vary between 4 g and 7 g depending on grind and bean density — a swing that can shift your final strength by nearly 40%. If you prefer working in coffee-to-water parts, the coffee ratio calculator turns “1:8 for 2 litres” into grams in one step.

Caffeine Yield: What You Actually Get Per Glass

Cold water extracts caffeine more slowly but very completely over a long steep. For a medium-roast arabica at about 1.2% caffeine by weight:

• A 1:8 concentrate brewed 16 hours yields roughly 65–75% of the bean’s caffeine — about 1.0 g of caffeine from 125 g of coffee.
• Diluted 1:1, that is roughly 135 mg per 250 ml serving — comparable to a double espresso.
• A 1:12 ready-to-drink brew lands nearer 90–110 mg per 250 ml, similar to a strong drip coffee.

The practical takeaway: dilution is where caffeine concentration is decided, not the steep time alone. If you want to compare a cold brew’s caffeine load against an energy drink or drip coffee as a percentage of a daily limit, the percentage calculator is handy for expressing mg against the commonly cited 400 mg/day reference.

Scaling the Batch Without Ruining It

1. Decide the drinking strength first, then work backwards to the concentrate ratio.
2. Multiply grams of coffee by batch size — 1:8 for 3 L needs 375 g of coffee, not 125 g.
3. Keep steep time constant: 14–18 hours at room temperature. Doubling water does not mean doubling time.
4. Grind coarse, like sea salt. Fine grounds clog filters and turn the brew bitter and muddy.
5. Strain through a paper filter after the initial mesh pass for a cleaner cup, then store chilled up to 7 days.

If you are also mixing flavoured syrups or cutting concentrates with milk, you are back to a dilution problem — the dilution calculator handles concentrate-to-serve ratios the same way it does for cleaning products and garden sprays.

Frequently Asked Questions

By weight or by volume? Weight. Coffee-to-water by volume is off by up to 30% because ground coffee traps air.

Room temperature or fridge? Room temperature steeps faster and extracts more; fridge steeping takes 18–24 hours and tastes rounder.

Can I re-steep the grounds? You can, but the second pass extracts mostly bitterness with little caffeine left.

Why is my cold brew sour? Usually under-extraction — too short a steep, too coarse a grind, or a ratio above 1:14.