The amount of weight you should lift on a dumbbell bench press depends on several factors. These include your size, existing strength and type of results you want to achieve. Safety is a top priority, and you should never lift more weight than your body can handle while maintaining proper bench press form and technique.
One Repetition Maximum
The amount of weight you should bench press with dumbbells is based on a percentage of the maximum amount of weight you can do for a single repetition. Your maximum single repetition weight is known as one repetition maximum, or 1RM. To safely lift weights while still building muscle, the amount of weight you should lift for your dumbbell bench press is generally between 60 and 80 percent of your 1RM. Testing your maximum weight limit by actually lifting the maximum amount of weight can be dangerous and lead to injury, so you have other ways to calculate your 1RM without putting yourself at risk.
The proper amount of weight to build muscle and increase endurance makes your muscles feel fatigued by the time you reach your last few repetitions. Fatigued muscles will burn a bit and you'll feel as if you almost can't complete your final rep or two. Depending on the results you want, you could perform anywhere from six to 15 or more repetitions.
Calculating your 1RM is possible by using an existing formula, and inputting the amount of weight you used and the number of repetitions you performed before your muscles felt fatigue. The American Council on Exercise offers a Weight Training Load Calculator that includes bench press calculations to determine your 1RM for a bench press with dumbbells. For instance, if your muscles felt fatigued after 10 repetitions of bench pressing 100 lb. with two 50-lb. dumbbells, your 1RM is about 133 lb., or 66.5 lb. for each dumbbell.
The type of muscle strength you’re trying to achieve plays a part in the number of repetitions and amount of weight you use. Strength endurance training works best with high repetitions of 15 or more and a light load of between 30 and 50 percent of your 1RM, according to sports coach Brian Mackenzie’s website. Power training uses fewer repetitions, or between six and 10, with loads between 70 and 80 percent of the 1RM. If you’re going for bigger muscles, train with eight to 10 repetitions using 70 to 80 percent of your 1RM.