One Rep Max Calculator: Estimate Your 1RM

Testing a true one rep max is risky and exhausting, so lifters use rep-based formulas to estimate it from a lighter sub-maximal set. All three formulas below take the weight you lifted (w) and the reps you performed (r) and extrapolate what you could lift for a single rep.

• Epley: 1RM = w × (1 + r ÷ 30)
• Brzycki: 1RM = w ÷ (1.0278 − 0.0278 × r)
• Lombardi: 1RM = w × r^0.1

Formula comparison

These are estimates, not guarantees. Different formulas can disagree by several pounds, and individual strength, fatigue, form and the specific exercise all shift the real number. Treat the result as a planning tool, not a promise.

Sources: Epley formula — Epley, B. (1985), "Poundage chart"; Brzycki formula — Brzycki, M. (1993), Strength Testing — Predicting a One-Rep Max from Reps-to-Fatigue; conversion factor 1 kg = 2.20462 lb. See also the National Strength and Conditioning Association.

You bench press 100 lb for 5 reps. Here is what each formula estimates:

• Epley: 100 × (1 + 5 ÷ 30) = 100 × 1.1667 = 116.67 lb
• Brzycki: 100 ÷ (1.0278 − 0.0278 × 5) = 100 ÷ 0.8888 = 112.51 lb
• Lombardi: 100 × 5^0.1 = 117.46 lb

With the Epley estimate of 116.67 lb, the estimated-max-reps table says you should manage about 92.11 lb for 8 reps (78.9% of 1RM), and the percentage table says 50% of 1RM is 58.33 lb — a typical warm-up or endurance weight.

Pick a recent set you performed close to failure on the lift you want to test — for example your last bench press or squat set — and enter it below. The calculator does the rest.

Step by step

After pressing Calculate you get the estimated 1RM, the full estimated-max-reps table (1 to 20 reps) and the percentage-of-1RM table (100% down to 50%). Use the Reset button to clear the results and try a different set.

The estimated max reps table answers "how much can I lift for N reps?" — each row is derived by inverting the Epley formula, so row 1 shows 96.8% of your 1RM rather than 100%. The percentage-of-1RM table answers the training question: "what weight is 80% of my max?"

Typical training zones

Most programs work with percentages rather than absolute weights, because percentages scale with your strength. When a program says "5 × 5 at 80%", look up the 80% row in the percentage table and load that weight.

Strength programs like 5/3/1, Starting Strength progressions and most periodized plans are written in percentages of your 1RM. Without knowing your max, "lift at 75%" is meaningless — the percentage tables above turn it into a number you can actually load on the bar.

Your 1RM is also a useful progress metric alongside body composition. If your max goes up while your body weight is stable, you are getting stronger pound for pound — and a BMI calculator gives you a quick read on where that body weight sits.

Strength gains are built on recovery as much as training. Protein intake drives muscle repair, so lifters tracking their 1RM often check a protein intake calculator to make sure their nutrition supports the numbers they are chasing.

Rep-based formulas are most accurate for 1–10 reps. Past 10 reps, fatigue and conditioning skew the estimate upward — the calculator flags these sets so you know to take the number with a grain of salt.

No formula knows your sleep, your form, or the exercise. Estimates from a leg press overstate your squat max; estimates from fresh morning sets overstate what you can do at the end of a long session. Retest every 8–12 weeks and adjust when real lifts beat the estimate.

Never attempt a true 1RM alone or without safety equipment. Use a spotter, safety pins or a power rack, warm up through the percentage table (50%, 70%, 85%) and stop a rep when form breaks down — the calculator is a planning tool, not a spotter.