Free Tool
Zone 2 Heart Rate Calculator for Rucking
Find your Zone 2 heart rate range using the Karvonen method and Tanaka HRmax. If you add your body weight and ruck weight, the tool also estimates a walking pace band that should land you inside the zone on flat pavement.
See how we calculate thisZone 2 Heart Rate Calculator
Karvonen method + Tanaka HRmax, with a Pandolf-derived pace band
Use your wake-up reading from Whoop, Garmin, Apple Watch, or a 7-day average for best accuracy.
208 - 0.7 × age. Validated across 18,712 subjects (Tanaka 2001, PMID 11153730). Default.
What Zone 2 is and why it matters for rucking
Zone 2 is the training intensity where you are working hard enough to drive aerobic adaptations - mitochondrial density, fat oxidation, capillary growth - but easy enough that you can hold a conversation. For most people, that translates to about 60-70% of heart rate reserve (HRR).
Rucking is one of the most efficient ways to hit Zone 2. The pack raises your heart rate at the same walking speed, which means you reach the right intensity without having to jog. That preserves joints and lets you train Zone 2 for longer than running allows.
How the calculator works
The HR target uses the Karvonen method: Target HR = ((HRmax - HRrest) × intensity) + HRrest. We default HRmax to the Tanaka formula (208 - 0.7 × age), the 2001 paper that replaced the older 220-age rule and has been validated against 18,712 subjects.
When you add body weight and ruck weight, the calculator back-solves the Pandolf load-carriage equation at the midpoint of your Zone 2 HR band to estimate a walking pace range on flat pavement. Trust the HR reading first - the pace is an estimate that drifts with terrain, heat, and individual fitness.
Why HR beats pace under a ruck
A 20 kg pack adds about 20 BPM at the same walking pace (Simpson et al. 2010, PMID 20962921). That is a huge shift - enough to push you out of Zone 2 even if your watch says you are walking the same speed as your unloaded routes. Looney et al. 2021 (PMID 33652153) found that heart rate reserve scales more predictably than VO2max under heavy loads, which is why wearable HR is the right primary target for ruck pacing.
Where this tool fits in your training
Use it for the slow, conversational rucks that should make up most of your week. For race pace, GORUCK event prep, or interval work, you want the upper zones - not this calculator. For weight loss, Zone 2 is the right target because long sessions at this intensity maximize total fat oxidation while staying recoverable.