1RM calculator

We earn a commission for products purchased through some links in this article.

Studies show training to a percentage of your 1RM could help you hit your goals.

Even after years of strength training, there are still times when I’m unsure how heavy my weights should be. Most advice is to take a subjective approach – you should increase or reduce the weight you lift based on how you feel, whether directly or inadvertently using the RPE (Rate of Perceived Exertion) scale. But that doesn't always work. Sometimes, I’ll go into the gym feeling like superwoman, ready to lift the world, before realising I can only do a couple of reps. Likewise, I might feel like I could sleep for England, then manage to lift heavier than ever. It's baffling.

Your 1RM (also known as one-rep max), on the other hand, is an objective measure of your training ability; it tells you exactly how heavy you are capable of lifting in ideal conditions. This number can help you identify specific rep ranges to achieve different goals, and with research showing that you’re more likely to underestimate how strong you really are when training based on RPE, PBT (Percentage Based Training, i.e., working to a percentage of your 1RM) could help you progress sooner.

Andy Vincent, a strength and conditioning coach tells us: ‘If you try to go off memory or how lifting a certain weight feels, you might end up lifting too much, or backing off miles too much, which can mean you can take much longer to progress. Working with your 1RM (or percentages of this) can be a great way to get you lifting the correct loads for each of your goals, sooner than if you were to rely on how you feel.’

That said, there are caveats. If you’re one of the 14.6k of you who search for 1RM calculators every month, you might want to read this.

‘Your 1RM is your one repetition max. It's the maximum weight you can lift for one rep. It's a test for maximal strength and is most typically performed on big compound lifts like squat, bench press, and deadlifts,’ Vincent explains.

You’ll be able to execute just one rep; a second will be a total no-no. In the same vein, a 2RM is the max amount of weight you can lift for two reps; 3RM is the most weight you can lift for three reps; 4RM is the most you can lift for four reps and so on.

In 2020, a meta-analysis looking into the reliability of test-retesting of your 1RM was published. It investigated how consistent 1RM results were for each participant, when variables such as the number of sessions each participant had done was changed, and it found that 1RM testing has ‘good to excellent’ reliability.

Sounds pretty solid, right? There's certainly something in max rep testing and training, but is attempting your 1RM really wise? Keep reading…

The easiest and most popular way to calculate your 1RM is to use an online calculator or formula.

‘There are a few formulas that you can use; the main ones being the Epley and Brzycki formulas, or you can use online calculators which work out these formulas for you,’ says Vincent. ‘With these, you can use the weight you use for rep ranges in your usual sessions to calculate a theoretical 1RM.’ So, for example, if you usually do 6 reps of back squats at 50kg, you will input this into an online 1RM calculator, which will then be used to calculate what your 1RM would be.

Top tip from Vincent: 'The further rep range you are from one, the less accurate the online 1RM calculations tend to be. I suggest not using anything over five reps to calculate. To work this out, you’ll need to test for your 5RM.' Read on for advice on how to do this in the safest – and most reliable – way possible.

Most online 1RM calculators are based upon the John Epley equation, which was created back in 1980, Vincent tells us. Here's how the equation goes:

So, let's say you typically back squat at 87.5kg for 5 reps. Here's how you would work out your 1RM.

Bashing out your 1RM involves pushing yourself to your absolute limit. You’ll recruit a huge amount of muscle fibres and put a massive amount of strain on your central nervous system, so you categorically must warm-up if you want to avoid injuring yourself.

Vincent's advice? ‘Whether you’re testing for your 1RM or going for a 3 or 5RM (which I would recommend, to help you work out your 1RM), you’ll still be lifting much heavier than usual. I would suggest doing 3-6 warm-up sets, gradually building up the weight to your target max.’

If your usual weight is 50kg, for example, implement progressive overload by incrementally increase the weight by 2 or 5kgs until you reach your max. Whatever you do, don't go full steam ahead and attempt to lift your max from the get-go.

1RM and PR are often confused, but here's how to differentiate the two:

A PR could also refer to rep ranges; 12 reps of a bench press might be your PR, but 10 reps might be your standard.

Now for the interesting bit. Recently, there has been a wealth of research on the efficacy of training to muscle failure using your 1RM in the interest of muscle growth (a.k.a. hypertrophy) or strength; it shows that, in fact, working with your maximum load isn't fundamental to progress, and the same results can be yielded without working to your maximum.

Vincent now rarely uses 1RM testing or training with his clients, adding that, aside from it not being essential for muscle mass and strength, ‘It's hugely taxing, and your chances of injury are very high.’ But the theory of using max repetitions still goes: ‘I would suggest working towards improving your 3RM or 5RM instead,’ Vincent advises. ‘This will be a lot less taxing, but you’re still lifting close to your 1RM.’

Here are his top tips for getting the most out of your 3RM and 5RM training.

Knowing your 1RM (or as close as) is all well and good, but using that number to determine how heavy you should be lifting according to your specific goal is, well, basically the whole point. As mentioned, research shows that PBT (Percentage Based Training), could help you progress faster than if you are to choose your weight based on RPE, so here's an overview of exactly what percentages you should be shooting for, as advised by Vincent.

Goal: Speed/power1RM percentage: ‘65-75%. You should perform sets of 3-6 reps, focusing on maximal power.’

Goal: Muscle growth/hypertrophy1RM percentage: ’70-85%. This will vary because you can build muscle at every weight, depending on your experience with weightlifting, but if we generalise and you execute sets of 6-12 reps, you should look to lift 70-85% of your max.’

Goal: Strength 1RM percentage: ’90-95%. It's a common misconception that you should lift 100% of your max load to build strength; it's smarter to train at 90-95%, to ensure you can maintain good form and technique. That said, I wouldn't recommend this unless you are extremely experienced.’

Goal: Endurance1RM percentage: ’60-65%. Again, this depends on your definition of endurance, but if you are aiming for around 15 reps per set, go for 60-65% of your 1RM. Just remember that percentages of your 1RM become less and less accurate as the reps performed move further from 1.’

By this point, it's probably pretty clear that, based upon the recent research, Vincent is an advocate of 3RM and 5RM training over 1RM. But if curiosity is getting the better of you, here are his pointers for testing for your 1RM as safely as you can. These also apply to testing for your 3RM and 5RM.

‘Honestly, I’d say the risk of executing your 1RM outweigh the rewards,’ Vincent affirms. ‘Stick to 3 and 5RMs; they’ll get you close enough to your 1RM for you to be able to work out the percentages and weights you should lift for your goals, while significantly reducing the risk of injury.

‘Doing three or five reps still allows you to build strength more effectively than if you were to do 8-10 reps. It's all about low volume and high load training. Doing a high volume of reps is what causes the accumulative fatigue that stops you from doing more, not your strength. If you reduce the volume you are doing, you’ll be able to lift more, and thereby build strength.

‘Always do these max rep sets at the start of a workout; you don't want to be fatigued when doing the hardest part of a session. And make sure you always do this; if you do them first one week, then at the end of your workout the next, your results won't be comparable, so you won't have a true picture of your progress.’

If you don't have experience with it at this point, probably not. Percentage-based training (PBT) is worth experimenting with, as studies show that it could help you achieve your goals sooner than RPE, if you don't feel that you’re as in tune with your body as you’d like to be. Your 3RM and 5RM are just as useful, without the risks that could come with your 1RM.

18 celebs who lift weights on the reg

Your guide to compound exercises and lifts

25 exercises to build a strong AF core from home

Victoria Beckham's full exercise routine debunked

The best pre-workout supplements for women

The complete strength training guide for beginners

Here's how to make your DOMS more manageable

Your back-to-basics resistance training guide

49 dumbbell exercises you need to be doing

29 Arm exercises to tone, tighten and strengthen

15 best deals on hand weights, from £5.99

'I switched from HIIT to weightlifting 1 year ago'