{
    "name": "One Rep Max Calculator",
    "url": "https://calculators.geekmidst.com/calculators/one-rep-max-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/one-rep-max-calculator.md",
    "category": "Health & fitness",
    "description": "Estimate your one-repetition maximum from a weight and the reps you managed, using the Epley and Brzycki equations, with a table of training loads.",
    "summary": "Your one-rep max (1RM) is the heaviest weight you could lift once. Instead of testing it, estimate it from a set of up to 10 reps taken close to failure.",
    "also_called": [
        "1RM calculator",
        "Max lift calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "weight",
            "label": "Weight lifted",
            "type": "number",
            "default": "100"
        },
        {
            "name": "unit",
            "label": "Unit",
            "type": "segmented",
            "default": "kg",
            "options": {
                "kg": "kg",
                "lb": "lb"
            }
        },
        {
            "name": "reps",
            "label": "Repetitions completed",
            "type": "number",
            "default": "5",
            "unit": "reps"
        }
    ],
    "outputs": [
        {
            "key": "one_rm",
            "label": "Estimated 1RM (average)",
            "format": "number"
        },
        {
            "key": "epley",
            "label": "Epley estimate",
            "format": "number"
        },
        {
            "key": "brzycki",
            "label": "Brzycki estimate",
            "format": "number"
        },
        {
            "key": "unit",
            "label": "Unit",
            "format": "text"
        }
    ],
    "formula": {
        "text": "Epley: 1RM = w × (1 + r ÷ 30);  Brzycki: 1RM = w × 36 ÷ (37 − r);  shown: the average of the two (a single rep is taken as the 1RM).",
        "variables": {
            "w": "weight lifted",
            "r": "repetitions completed with good form"
        }
    },
    "worked_example": {
        "inputs": {
            "weight": "100",
            "unit": "kg",
            "reps": "5"
        },
        "steps": [
            "Epley: 100 × (1 + 5 ÷ 30) = 116.7 kg.",
            "Brzycki: 100 × 36 ÷ (37 − 5) = 112.5 kg.",
            "Average: (116.7 + 112.5) ÷ 2 ≈ 114.6 kg."
        ],
        "result": "Five reps at 100 kg suggests a one-rep max of roughly 113–117 kg, about 114.6 kg on average."
    },
    "interpretation": "Treat the estimate as a planning number, not a target to attempt. The table converts it into common training loads, for example 80–85% of 1RM for sets of about 5–6.",
    "assumptions": [
        "The set was performed with consistent technique and taken close to muscular failure.",
        "The equations were developed mainly on trained adults performing barbell lifts."
    ],
    "limitations": [
        "Accuracy falls as reps rise; above about 10 reps the equations can be off by 10% or more.",
        "Results vary by lift and by person: endurance-trained lifters often manage more reps at a given percentage than strength-trained lifters."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Which formula is more accurate?",
            "answer": "Neither is consistently better. They agree exactly at 10 reps; below that, Epley gives slightly higher numbers. Averaging them is a reasonable middle estimate."
        },
        {
            "question": "Is it safe to test a true 1RM?",
            "answer": "Maximal attempts carry injury risk, particularly without a spotter or coaching. An estimate from a 3–5 rep set avoids that risk for most training purposes."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "Target Heart Rate Calculator",
            "url": "https://calculators.geekmidst.com/calculators/target-heart-rate-calculator"
        },
        {
            "name": "Protein Calculator",
            "url": "https://calculators.geekmidst.com/calculators/protein-calculator"
        },
        {
            "name": "TDEE Calculator",
            "url": "https://calculators.geekmidst.com/calculators/tdee-calculator"
        },
        {
            "name": "Percentage Calculator",
            "url": "https://calculators.geekmidst.com/calculators/percentage-calculator"
        }
    ],
    "disclaimer": "This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health.",
    "publisher": "GM¹X CalcVerse"
}