“When is blood pressure high enough to go to the hospital?”

When you are experiencing symptoms such as headache, fussiness, nausea or vomiting chest pain, etc. If you don’t have symptoms avoid processed and fast foods. Added salt. Make an appt with your doctor. He will help you manage it.

180/120 and have chest pain, shortness of breath, numbness, weakness.

It's not just the number you have to think about.  It's the symptoms you are having with the high number.  Some people can tolerate a systolic (the first number) of 200, whereas some people may be having heart problems if their systolic is 160.  Just having a high number is rarely a justifiable reason to go to the emergency room for treatment.  But, if you are having chest pain, severe headache, sudden difficulty moving your arms or legs, sudden difficulty speaking, severe dizziness, sudden severe upper back pain, or difficulty breathing, you need to go to the emergency room regardless of your blood pressure.  Perfect blood pressure is systolic under 120, but most people are often higher than that and can tolerate a number higher than that without difficulty.