if you use an iPhone, you can download an app called BulletDrop+. I've used it for years. I've also used an app called iStrelok for years. BulletDrop is just a bullet drop chart you input data, it does the calculations, and gives you drops and dopes. Strelok you input your rifle's data and your scope's data, and it shows you on your reticle, your drops. You can also manipulate your zero, max yardage, etc... Between the 2, you should find one that works for you.
But it sounds like you're wanting a basic bullet drop compensation calculator, in which case, BulletDrop+ is what I recommend.