Thermal Loss Calculator

The kettle says 96 °C; the V60 was on the shelf at 20 °C. They meet, and the slurry is cooler than you think. This is a two-body mix: water mass and heat capacity versus vessel mass and Cp (ceramic is not plastic). Preheat if the drop hurts extraction; skip the ritual if the math says a degree.

Inputs

Units

Results

Mixed temperature: 82.0°C
Drop from kettle: 14.0°C

Recommended gear

Fellow Stagg kettle
Hold-temp kettles keep waterTempC honest while you weigh the vessel. A rolling boil on an open kettle is already dropping.
Typical range: $150–$200
Barista thermometer
Spot-check the slurry if you do not trust Cp. One measured drop calibrates the guess.
Typical range: $8–$25
Hario V60 dripper
Plastic V60s steal less heat than thick ceramic. Weigh yours; that mass is the input.
Typical range: $10–$40

Calculation method

Energy conservation: water at 4.184 J/g·K mixes with the vessel at your Cp. Final temperature is total enthalpy over total heat capacity. Drop is kettle temperature minus that mix. 250 g at 96 °C into 280 g ceramic at 20 °C and 0.84 J/g·K lands several degrees cooler — enough to notice on a light roast, not enough to explain a completely dead cup.

Exact formula

tFinalC = (waterMassG × waterTempC × 4.184 + vesselMassG × vesselTempC × vesselCp) / (waterMassG × 4.184 + vesselMassG × vesselCp). dropC = waterTempC − tFinalC. vesselCp defaults to 0.84 (ceramic) if omitted. Limits: Evaporation, room loss during the pour and bed mass omitted; Cp is a guess unless you measured it.

Bloom temperature

The first 40 g of bloom sees the worst drop. That is why people rinse paper and preheat — not because it is romantic.

Frequently asked questions

Do I include the coffee bed?

Not in this version. Grounds add mass near room temperature. Treat this as dripper/server only, then expect another small drop.

Preheat water — count it?

If you dump the preheat, vesselTempC is higher and vessel mass may be wet. Weigh and measure after preheat for a fair run.

Iced coffee?

Ice is a huge sink. Use the flash-brew tool for recipe ice; this page is for hot vessels.

Disclaimer — no professional advice, no liability

This is lumped thermal mixing, not a CFD of your cone. A wet, preheated dripper is a different vesselTemp. If the cup tastes dull and sour, grind and ratio still come before blaming a 2 °C drop.

These calculators, pages and any related content are provided “as is” and “as available”, solely for general educational and informational purposes. They are simplified mathematical estimates, not a cupping score, a water lab report or a roasting profile, and they do not constitute professional barista, roasting, food-safety or medical advice.

Results can be wrong, incomplete or inapplicable to your grinder, brewer, beans, water or use case. You must independently verify every figure, assume all risk, and confirm on a test brew before you scale a recipe, descale a machine or change caffeine habits. Hot water, steam and espresso equipment can scald; caffeine calculators are not a substitute for medical care.

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Thermal Loss Calculator

Inputs

Results

Recommended gear

Calculation method

Exact formula

Bloom temperature

Frequently asked questions

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