Now we are talking about an estimated rise of eustatic sea level of about 3mm per year. Over the last 100 years sea level has probable risen about 10-15cm. This is difficult to measure. Some areas of the world are isostatically rebounding after earlier glaciation and show a relative sea level decrease. Others are subsiding tectonically.
Data come from tide gauge measurements.
We have new orbiting radar gun for more precise measurement. Best estimate of sea level rise is 17-26 cm between 1985 and 2030. This is a rate of change that may be 2-6 times faster than rate of change over the last 100 years. Most concern is about the rate of change and not the amplitude of change. Volume of oceans increases as they warm.