Megan Falk joined the Shape.com team in 2019 and serves as the assistant editor, primarily covering exercise tips, fitness modalities, workout trends, and more. Previously, she was Shape’s editorial assistant and covered food trends and nutrition, sustainability, health and wellness, and beauty topics, among others. Before joining the team, Megan worked as an editorial intern at DoctorOz.com. Megan graduated with a bachelor’s degree in magazine journalism and a minor in food studies from the S.I. Newhouse School of Public Communications at Syracuse University. Her writing has also appeared in Health, SAVEUR, her hometown’s magazine, Hour Detroit, and more. She’s currently preparing to earn her personal trainer certification through the American Council on Exercise.

If you've been lifting weights on the reg, you probably have a rough idea of just how far your muscles will take you. You might know you're capable of banging out at least eight reps on a leg press machine that's set at a weight that requires a She-Hulk-level of strength. Or, you may know that your chest muscles are strong enough to press dumbbells that are the same weight as your dog at least three times.

But if you want an exact measurement of your absolute strength, consider testing your one-repetition maximum — aka one-rep max. Here, fitness experts break down everything you need to know about the strength-training tool, including its key perks for your training program and how to safely perform those Herculean lifts.

To break it down, a one-rep max is the absolute greatest amount of weight you can lift for one single rep of a particular exercise — with proper form, of course, says Natalie Smith, C.P.T., a certified powerlifting coach-practitioner in Portland, Oregon. You'll typically test your one-rep max during compound lifts, multi-joint movements that call on multiple muscle groups at the same time. Think: the back and front squat, deadlift, and bench press, she says. "When more muscle groups are working together, you're going to be able to lift more weight, so it makes more sense to use one-rep maxes in that application," she adds. It's also common to check your one-rep max for Olympic weightlifting exercises (such as the snatch and the clean and jerk), adds Laura Su, C.S.C.S., a strength coach in Seattle.

While you can perform one-rep maxes with accessory exercises (re: single-joint movements, such as the biceps curl or bent-over row), it's not typically necessary if you're already performing those compound movements, says Su. "You'd be getting that maximal stimulus through compound lifts well enough," she explains. "Then, you can simply use the accessory lifts to add or keep volume training in your program since you wouldn't get as much volume when testing a one-rep max."

Understanding your one-rep max is crucial if you're involved in powerlifting — a competitive sport that involves testing your absolute strength in the bench press, squat, and deadlift, specifically, says Su. In fact, the goal of the sport is to have the highest one-rep max for each of those movements, adds Smith. But occasionally testing your one-rep max on compound lifts can be beneficial even if you're just a casual strength exerciser.

Not only does testing your one-rep max allow you to measure your progress over time, but it also shows you just how strong you truly are at a particular point in time. And that knowledge can be valuable for strength-training newbies, says Su. "It's a good idea to test your one-rep max after [you've spent] some time of training and you've established your technique and form," she explains. "It gives you an idea of like, 'Oh, I'm actually a lot stronger than I thought I was. I could be pushing weights during my regular lifts a little bit harder.'"

What's more, successfully squatting a monstrous barbell can make you feel like a total badass, adds Smith. "One of the most overlooked aspects of strength training is the psychological component," she explains. "When you get to see how strong you are and reflect on all of your progress — maybe you're lifting more weight than you ever thought possible — that's really empowering."

Once you know your one-rep max, you can use it to determine the amount of weight you should be using in other aspects of your training. In a well-structured strength-training program, you'll work through various phases in which you focus on different qualities, such as increasing volume or building strength, says Smith. In each phase, the weight you use can be determined based on a percentage of your one-rep max, she explains.

To encourage hypertrophy (aka muscle growth), for example, you'll generally perform six to 12 reps of a particular exercise with a weight that's 67 to 85 percent of your one-rep max weight, according to the American Council on Exercise (ACE). So if your one-rep max for back squats is 100 pounds, you'll use a barbell that weighs 67 to 85 pounds to encourage those gains. To build muscular endurance, you'll typically perform more reps using a load that equates to 67 percent of your one-rep max weight, according to ACE. "You want to spend more time building strength than you do testing it [with one-rep maxes]," says Smith. "Using percentages allows you to have a guideline of how much weight to use, so that you're not just constantly going way too heavy or failing lifts all the time."

If you don't currently have access to heavier weights or the proper safety equipment (or spotters), you can use a few tools to estimate it. First, you can use online calculators, such as one from the National Academy of Sports Medicine, which bases your estimated one-rep max on the weight you use and the number of reps you can do for an exercise. Or, you can look to your five-rep max, which is typically seen as 87 percent of your one-rep max, says Su. For example, if you can deadlift just over 60 pounds for five reps, your estimated one-rep max for the exercise would be 70 pounds. If you don't want to do all the math yourself, look to this handy chart from the National Strength and Conditioning Association, which can help you find your estimated one-rep max based on the weight you're using and your max number of reps.

On the flip side, you can use the Brzycki prediction equation, a formula commonly used in exercise science studies, to estimate your one-rep max, if you feel like breaking out your calculator. In this formula, one-rep max = weight used in kilograms / [1.0278 – .0278 (max number of repetitions performed)]. Let's say you can bench press 25 kilograms (about 55 pounds) for six reps. Using this equation, your one-rep max for the exercise would be roughly 29 kilograms (nearly 64 pounds).

Just know that the online calculators, charts, and formulas may not be totally error-proof, and factors such as technique, gender, age, and how well you've recovered from your previous workout can all impact your one-rep max, says Smith. "The only way to really know what your one-rep max is to test it, but they can be a helpful tool," she says.

If you're ready to test your one-rep max, don't walk into the gym, load the barbell with as many weights as possible, and try lifting it with all your might, says Su. First, you'll need to properly prepare your body for the heavy lift to come. "You want to strategically warm up in a way that you're minimizing the amount of fatigue and priming yourself as much as you can to lift a heavy weight," she explains.

Start by performing a few mobility drills to loosen up your joints, then do your first set with just a barbell, says Su. If you're using dumbbells, begin with a pair that weighs about 50 percent of your estimated one-rep max, according to ACE. After each set, increase the weight by 10 to 15 percent and reduce the number of reps, she suggests. As the load nears your estimated max weight, increase the load by just 5 to 10 percent and perform just one rep until you reach your max, she says. Try to perform no more than eight sets in order to keep fatigue to a minimum, she adds. Between each set, consider taking a three- to five-minute break to give your muscles enough time to recover from the strenuous lifts, adds Smith.

Here's an example of how Su might work her way up to her one-rep max for a barbell back squat:

Ideally, you'd want to have a spotter or two on-hand while testing your one-rep max for a squat or bench press, as you can get stuck at the bottom of the movement, says Su. In that instance, they'd be able to help you lift the weight up if you fail on a heavy rep, she adds. If that's not an option for you, use a rack that has safety pins and place them an inch or two below the lowest point of your squat or chest press. If you need to bail out of a move, just rest the bar on the pins, she says. A deadlift, however, is generally safe enough to do solo, as you can simply drop the weight if it feels too heavy, she says.

Considering that BAMF feeling you get after testing your one-rep max, it may be tempting to incorporate them into your routine on the reg. But Smith cautions against doing so. "True one-rep maxes shouldn't make up the majority of your program, because if you're always testing your strength, you're a lot more likely to injure yourself," she says. "If you're constantly testing the same thing, you're also not going to be making any progress." That's why she recommends capping your one-rep max checks to once every eight to 12 weeks.

During that time period, you should focus on building up your strength and training using weights in those lower percentages, says Smith. Start off lifting with a lower weight for a higher number of reps. Then, gradually increase the load and go easy on the reps to build up strength as you approach your testing day, she suggests. For a more personalized plan, consider working with a strength coach, who can ensure you're taking all the necessary steps to meet your fitness goal.

When your next assessment rolls around, don't expect to see a massive jump in the weight you can lift. "Some people will think, 'Oh, maybe I can hit like a 50 or 60 pound PR' — that's not usually very realistic," says Smith. Instead, you can expect to go up just five to 10 pounds from your last one-rep max, which is still an incredible feat. "If you can consistently add five pounds to your lift, that's going to add up to a lot, months and years down the road," she says. "So be patient with it — building strength is a marathon, not a sprint."

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