Free One Rep Max (1RM) Calculator
Estimate the maximum weight you can lift for a single rep. Enter a weight and rep count from a recent set to get your projected 1RM using 7 proven formulas.
What is a One Rep Max (1RM)?
Your one rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It is the standard measure of absolute strength in weight training and powerlifting. Knowing your 1RM lets you set precise training loads, track strength progress over time, and compare performance across exercises.
Rather than testing your true max in the gym — which carries injury risk and requires significant recovery — most lifters estimate their 1RM from a submaximal set. You perform a set at a challenging weight, note how many reps you completed, and use a formula to project what your single-rep max would be.
How to use your 1RM for training
Most structured strength programs prescribe weights as a percentage of your 1RM. For example, a program might call for 5 sets of 5 reps at 80% of your 1RM. This percentage-based approach ensures the load is appropriate for your strength level and the session's training goal — whether that is maximum strength, muscle growth, or endurance.
The training load chart in the results section above converts your estimated 1RM into working weights for each training zone. Use it to plan your sets without guesswork.
The formulas
This calculator includes seven established 1RM prediction formulas. Each uses a slightly different mathematical model, but all take the same two inputs: weight lifted and reps performed.
Epley: 1RM = weight × (1 + reps / 30)
Brzycki: 1RM = weight × 36 / (37 − reps)
Epley and Brzycki are the most widely used. They give nearly identical results at 10 reps and diverge slightly at higher rep counts. The remaining five formulas (Lander, Lombardi, Mayhew, O'Conner, Wathen) use variations of linear, polynomial, and exponential models. The "Average" option combines all seven for a more stable estimate.
How accurate are 1RM calculators?
These formulas are most reliable when you use a weight lifted for 2 to 10 reps. In that range, trained lifters can expect estimates within about 5% of their true tested max. Accuracy decreases above 10 reps because muscular endurance and fatigue tolerance play a larger role. Individual factors like training experience, muscle fiber composition, and exercise technique also introduce variation.
For the most accurate result, use a recent set where the last rep was genuinely challenging — close to failure, but with clean form.
Track Your Estimated 1RM Automatically
Slate estimates your one rep max from every set you log — no manual calculation needed. Watch your projected max climb over weeks and months as you get stronger.
Download Free for iOSFrequently Asked Questions
Perform a set of an exercise at a challenging weight for multiple reps (ideally between 2 and 10). Enter the weight you lifted and the number of reps you completed into the calculator above. The calculator applies proven formulas like Epley and Brzycki to estimate the maximum weight you could lift for a single repetition.
1RM calculators are most accurate when you use a weight you can lift for 2 to 10 reps. In that range, most formulas predict your true 1RM within 5% for trained lifters. Above 10 reps, accuracy drops because muscular endurance becomes a bigger factor. Individual differences in muscle fiber composition, training history, and technique also affect accuracy. For the best estimate, use a weight that challenges you in the 3 to 6 rep range.
Direct 1RM testing carries more injury risk and requires proper warm-up protocols, a spotter, and experience with heavy singles. For most lifters, estimating from a submaximal set is safer and practical enough for programming purposes. Direct testing makes sense before a powerlifting meet, after a peaking cycle, or when you have experience handling near-max loads. If you do test directly, work up gradually over 5 to 6 progressively heavier singles.
No single formula is universally best. Epley and Brzycki are the most widely used and produce nearly identical results at 10 reps. Brzycki tends to be slightly more conservative, while Epley is slightly more generous at higher rep counts. The Average option in this calculator combines all seven formulas for a more robust estimate. For low-rep sets (2 to 5 reps), most formulas agree closely. The differences become more noticeable above 10 reps.
For programming purposes, re-estimating your 1RM every 4 to 8 weeks is a good cadence. This aligns with typical training block lengths. You don't need to max out each time — just perform a heavy set of 3 to 5 reps and use a calculator. Many lifters update their training max (often set at 85 to 90% of estimated 1RM) at the start of each new training cycle.
It depends on your goal. For maximum strength, train at 85 to 100% of your 1RM for 1 to 5 reps. For muscle growth (hypertrophy), use 65 to 85% for 6 to 12 reps. For muscular endurance, use 50 to 65% for 15 or more reps. Most strength programs use a mix of these zones across the training week. The percentage chart above this section gives you exact working weights based on your estimated 1RM.