# 1RM Calculator | Forge > **Quick Answer:** The Forge 1RM Calculator estimates your one-rep max from any set: weight, reps, and how many reps you had left in the tank. It runs seven published formulas (Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner, Wathen) and headlines their average, then shows the right load for every rep count. Free and ungated. Example: 225 lb for 5 reps to failure estimates a max of about 260 lb. **dateModified:** 2026-08-09 --- ## Key Facts - **What it does:** Estimates one-rep max from any set of 1 to 30 reps - **Formulas:** Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner, Wathen. The headline number is the average of all seven, with the full spread shown. - **Reps in reserve:** Tell it how many reps you had left and it adds them to your completed reps before running the math - **Units:** lb and kg - **Extras:** A load chart for 1 to 20 reps, built from the consensus reps-to-percentage table - **Best accuracy:** Heavy sets of 2 to 5 reps on compound barbell lifts - **Cost:** Free. No sign-up. --- ## How to Use It 1. Pick lb or kg. 2. Enter the weight you lifted. 3. Tap how many reps you completed. 4. Tap how close to failure you went. "All out" means zero reps left. 5. Read the big number. That is your estimated max, averaged across seven formulas. The load chart under the result converts your max into a weight for every rep count. A program that says 3 sets of 3 at 90% turns into a number you can load on the bar. --- ## How the Math Works Seven published rep-to-max equations, computed exactly as written: Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner, and Wathen. The headline is the arithmetic mean. The spread runs from the lowest estimate to the highest, and a tight spread means you can trust the number. Every formula assumes the set ended at failure. Stopping with reps in the tank hides strength from the math, so the calculator adds your reps in reserve to your completed reps first. Five reps with two left runs as a seven-rep effort. With Epley, 100 kg for 5 to failure estimates 116.7 kg. The same set with two in reserve estimates 123.3 kg. Same bar, different max, and the second number sits closer to the truth if you honestly had two left. Accuracy is highest at low reps and softens past about ten, where muscular endurance starts to matter more than maximal strength. The equations were built on squat, bench, and deadlift data, so treat the output as well calibrated for the big barbell lifts and rougher on machines and isolation work. This is a planning tool. Never attempt a true max without a warm-up, a spotter or safety bars, and the experience to bail on a missed rep. --- ## Frequently Asked Questions ### What is a one-rep max? Your one-rep max is the most weight you can lift once with good form. Programs prescribe working weights as percentages of it, so it anchors almost everything in strength training. Testing it for real is fatiguing and carries some risk, which is why most lifters estimate it from a heavier set of several reps instead. ### Which 1RM formula is the most accurate? No single formula wins across the board. Validation studies find the best one shifts by exercise, sex, and rep range. Mayhew and Wathen tend to grade well on bench, Wathen on squat, and nearly every formula underestimates the deadlift. That is why this calculator headlines the average of all seven and shows you the spread. ### What if I didn't go all the way to failure? Tell the calculator how many reps you had left. Every formula assumes the set ended at failure. Stop a set of 5 with 2 in reserve and your effort was worth 7 reps. The calculator adds your reps in reserve to your completed reps before running the math, which keeps the estimate honest. ### How many reps should I use for the best estimate? Two to five. Accuracy is highest at low reps and softens past about ten, where muscular endurance starts to matter more than maximal strength. A heavy set of 3 to 5 taken close to failure gives the tightest estimate. ### How do I use the load chart? Each row shows the weight you could lift for exactly that many reps, based on your estimated max. Programs written in percentages translate straight off the chart: 3 sets of 3 at 90% becomes a plate-loaded number. These rows are all-out efforts, so everyday working sets should sit a little below the chart value. ### Should I just test my real 1RM instead? An estimate is safer and nearly as useful for most lifters. A true test needs a thorough warm-up, a spotter or safety bars, and experience bailing on a missed rep. Powerlifters peaking for a meet test under those conditions. Everyone else does fine estimating from a heavy set of 3 to 5 and re-checking every few weeks. --- ## Forge Tracks Your Maxes For You Forge is an AI personal trainer for iOS and Android. It builds an adaptive plan around your goals, schedule, and equipment, logs every set, estimates your maxes as you go, and sets the next weight target before you touch the bar. You get 4 trainer personalities and a 24/7 trainer chat. Pricing: $19.99/month, $59.99/year, or $6.99/week. All plans include a 7-day free trial. - **App Store:** https://apps.apple.com/us/app/forge-ai-personal-trainer/id6758403402 - **Google Play:** https://play.google.com/store/apps/details?id=com.tendylabs.forge - **Website:** https://forgetrainer.ai --- *https://forgetrainer.ai/tools/1rm-calculator*