You shouldn't be big at all. At five weeks pregnant you have just developed an embryo. An ultrasound typically will not even be able to detect a heartbeat yet.
If you mean 4 weeks after conception the embryo is about 1/6 to 1/4 inch (4 to 6 millimeters) long.
it takes four weeks for the organs of an embryo to form..
how big is the embryo when you began to hear its hearbeats?
An unborn baby that is less than 8 weeks old, is an embryo, after this it is classified as a foetus.
Your baby is 15 inches long and about 3 pounds!
Twenty-six weeks is six months.