Calcflux

Calcflux is a free collection of unit converters and calculators built for speed. It covers more than 2,000 conversion pairs across 13 categories - length, weight, temperature, volume, cooking, digital storage, pressure, fuel economy and more - plus calculators for mortgages, compound interest, BMI, body fat, protein intake, percentages, dates, and electronics such as LED resistors and EV charging cost.

What makes it different: every result shows the formula behind it, so you can check the math instead of trusting a black box. Pages load in under two seconds with no popups or interstitials. Cooking conversions account for ingredient density (a cup of flour is not a cup of sugar). Available in English, German, Spanish, French, and Portuguese, and every calculator can be embedded on your own site for free.