How accurate are the RunBikeCalc calculators?

RunBikeCalc calculators use validated sports science formulas: the Jack Daniels VDOT system for running pace zones, the 95% of FTP standard for cycling threshold power, and the Karvonen formula for heart rate zones. Results are accurate within ±3-5% for most athletes under normal conditions. Individual variation from lab-tested values is expected — use calculator results as a starting baseline, then adjust based on how you actually feel at those intensities during training. For racing, always verify paces in training before committing to a race plan.

What is the difference between heart rate zones and power zones?

Heart rate zones (typically 5 zones based on max HR or lactate threshold HR) reflect cardiovascular effort — useful for all endurance activities. Power zones (7 zones based on FTP) measure actual work output in watts — available only on bikes with power meters. Power zones respond immediately to effort changes; heart rate lags 30-90 seconds. For steady-state riding, both methods produce similar training stress. For intervals, power is more precise. Beginners should start with HR zones (cheaper, sufficient); serious cyclists wanting performance data should invest in a power meter.

How do I find my FTP (Functional Threshold Power)?

The most common FTP test: warm up 20 minutes, then ride all-out for 20 minutes, take 95% of your average power as your FTP. Alternative: the 8-minute test (2 × 8 minutes all-out, rest 10 minutes between, take 90% of the higher effort's average power). Ramp tests (increasing power every minute until failure) are popular on smart trainers and typically correlate to within 5-10% of traditional FTP tests. FTP typically improves 10-20% in the first training year and 3-5% annually for experienced athletes. Retest every 6-8 weeks during a training block.

Redirecting to LTHR Calculator...

The gear these numbers assume

Every pace, zone and power figure on this page assumes something is measuring it. These are the three that cover running, cycling and the threshold work in between.

Garmin Forerunner 965

Multisport with the training-load and threshold metrics most of these calculations assume you can actually see day to day.

Check Backcountry → Check price on Amazon →

COROS APEX 2 Series GPS Watch

Sapphire titanium and the longest battery in its class, which is the deciding feature once sessions run past a few hours.

Check Backcountry → Check price on Amazon →

Favero Assioma Uno Power Meter Pedal

Single-sided pedal power, the cheapest honest way to start training with watts instead of estimating from heart rate.

Check Backcountry → Check price on Amazon →

As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. Prices change, so check before buying.

LTHR Zone Calculator

The gear these numbers assume