How many weeks pregnant do you have to be to see anything on ultrasound?

5-6 weeks from LMP. The gestational sac is seen earlier than a fetus can be detected on an ultrasound. A gestational sac can be seen as early as the 5th week of pregnancy or 3 weeks after conception. If no gestational sac is seen, it could mean that you ovulated late. If HCG levels are less than 1100, repeat ultrasound should be obtained.
It varies. Pretty safe to say that by 5 weeks you will often see something indicative of pregnancy but will depend on equipment.
5-6 wks minimum! . Dates are expressed as time from the first day of your last period (lmp). It is assumed that conception took place around day 14-15 of your cycle. By 5 weeks it may be possible to see a tiny sac like structure on transvaginal (tv) scanning. By 6 weeks it is more likely that an early gestational sac may be more confidently identified. Between 6 and 7 weeks early heart activity may be seen.