If you don't have the space for a full set of dumbbells at home, consider Powerblock U-90 adjustable dumbbells. There are three stages in the U-90 series: stage I has a weight range of 5-50 pounds and replaces 16 pairs of normal dumbbells, stage II has a weight range of 5-70 pounds or 5-90 pound and replaces 22 and 28 pairs of dumbbells respectively, and stage III has a weight range of 5-125 pounds replaces 34 pairs. You can expand stage I and II to a higher stage. Changing weight is like changing the plates of weight machines in the gym i.e. by moving the weight selector pin into the appropriate slot. Color coding makes selecting the right slot easier. Prices start at $379 for stage I, $638 for stage II, and $937 for stage III. They're a good value for money compared to buying all the dumbbells they replace.