Does sweating more mean you burned more calories?
No. Sweating is thermoregulation — your body shedding heat — not a measure of work done or energy used.
When core temperature rises, sweat glands release fluid onto the skin. The cooling comes from evaporation, not from the sweat itself. This is why humid conditions feel so much worse: the air is already near saturation, evaporation slows, and you sweat more while cooling less effectively.
Several things determine how much you sweat that have nothing to do with effort:
Ambient temperature and humidity. A gentle walk in 32°C heat produces far more sweat than a hard interval session in a cold room.
Fitness level. Counterintuitively, fitter people sweat more, and sooner. Training improves thermoregulation, so the body starts cooling earlier and more efficiently. A well-conditioned athlete may be drenched while a beginner working much harder relative to their capacity is barely damp.
Individual variation. Sweat rate differs enormously between people for genetic reasons, and by body size, sex and acclimatisation.
Clothing. Non-breathable fabric traps heat and moisture, producing more sweat and less cooling.
Why the myth persists is largely the hot yoga and sauna-suit market. Weight lost during a sweaty session is water, and it returns as soon as you rehydrate. It is not fat.
Deliberately restricting cooling is counterproductive and can be dangerous. Heat exhaustion and heatstroke arise precisely when the body cannot shed heat fast enough.
Better measures of training effort are the load you moved, the pace you held, how long you sustained it, and heart rate — all of which relate to work performed rather than heat produced.