Free Health & Fitness Calculators — VO2 Max, Heart Rate Zones & More

Most fitness metrics that matter — aerobic capacity, training intensity, hydration, running efficiency — can be estimated from a handful of inputs using well-validated formulas. These calculators put those formulas in one place so you can answer specific questions without digging through research papers or buying a lab test.

Aerobic fitness — The VO2 Max Calculator estimates your maximal oxygen uptake from a sub-maximal test (resting heart rate + age, or a timed run). VO2 max is the single strongest predictor of cardiovascular longevity, so knowing your number gives you a meaningful baseline to track over time.

Training intensity — The Heart Rate Zone Calculator converts your max heart rate into five training zones (recovery through VO2 max effort). Training in the right zone for each workout is more effective than going hard every session — zones give you a prescription, not just a pace.

Hydration — The Hydration Calculator estimates daily fluid needs based on body weight, activity level, and climate. Mild dehydration (1–2% body weight) measurably impairs endurance performance and cognitive function long before you feel thirsty.

Running — The Running Pace Calculator converts between pace, speed, and finish time for any distance. Use it to plan a race strategy, set a treadmill speed, or check whether your training paces match your goal race.

All calculations use peer-reviewed formulas (ACSM, Mifflin-St Jeor, and similar). No account required, no data stored.