OrcaCalc

OrcaCalc is a free library of 153 calculators and unit converters for home projects, money, health, school and everyday math. Every page shows the exact formula, works through an example and links its sources (NIST, CFPB, CDC, extension services), so you can check the math. It covers concrete, gravel, decking, fencing and paint estimates with bag counts, mortgage, loan and compound interest, BMI and TDEE, GPA, and quick conversions like inches to cm. No sign-up and no ads, and your inputs never leave your browser.