Specific Heat Calculator
The heat needed to warm something up (or released cooling down).
The formula
Q = m × c × ΔT
Warming a kilogram of water from 20 to 100°C takes 335 kJ. A negative ΔT gives negative Q: the same energy comes back out when it cools. Melting and boiling are a different beast entirely; that's the latent heat calculator.
Water is the outlier
At 4,186 J/kg·K, water holds several times more heat than metal or rock. That single number explains coastal climates, why radiators use water, and why the kettle is the slowest appliance in the kitchen.