Eden's Fantasy:
Sex toys from adult toys store EdenFantasys
gives what appears to be reasonably good estimates of insertable length and circumference for dildos and other toys. They have reviews, ratings, and you can rank similar items by sales frequency.
The site allows you to visualize the toys full size in 2 dimensions on your monitor. You may need to adjust the size on your display to match the size of a 6 inch ruler, credit card, or dollar bill shown on the monitor.
A lot of sites give overall length measurements, for dildos as an example, that include a suction cup base, battery compartment, fake scrotum, or some other non-insertable component.