Faster running comes from running at the right pace, on the right day — not from running hard every time. This guide ties together the two anchors every runner needs: pace (the number on your watch) and zone (the effort underneath the number). When they agree, training works. When they fight, something is off.
Quick Answer
- Easy days belong in Zones 1–2 — at conversation pace.
- Tempo days sit at Zone 3 / threshold pace — comfortably hard, sustainable for ~30–60 minutes.
- Intervals push into Zones 4–5 — short, hard, fully recovered between bouts.
- 70–80% of weekly volume should be easy. That's the part most people get wrong.
Use our Running Pace Calculator for pace and race predictions, and our Heart Rate Zone Calculator for the underlying zones.
Pace vs. Zone — Why Both Matter
Pace is mechanical: distance over time. Zone is physiological: how hard your aerobic and anaerobic systems are working at that pace.
The same 5:00 /km can be Z2 endurance for one runner and Z4 threshold for another. As you get fitter, your Z2 pace gets faster while your heart rate at that pace stays the same. Tracking both numbers shows real improvement even when the scale says nothing changed.
Calculating Your Pace
Pace per kilometre is simply time divided by distance.
Pace = total time / distance
A 50:00 10 km → 5:00 /km → 8:03 /mile.
Our Running Pace Calculator handles km/mile conversion and includes preset distances (5K, 10K, half-marathon, marathon).
Race-Time Prediction (Riegel)
Once you have a race result at one distance, Riegel's formula projects times at others:
T₂ = T₁ × (D₂ / D₁)^1.06
The 1.06 exponent captures the small "endurance drag" of longer distances. A 25:00 5K predicts:
- 10K ≈ 51:48
- Half ≈ 1:54:33
- Marathon ≈ 3:58:38
Two caveats:
- Riegel assumes you are trained for the target distance. A fit 5K runner without long-run mileage will not hit the predicted marathon.
- The formula is most accurate within roughly 2× the input distance.
Our pace calculator runs Riegel automatically.
Splits — The Practical Side
A "split" is the time to cover one km or one mile. Holding goal pace inside a target time is the everyday job of pacing.
A 4:00 marathon → ~5:41 /km → ~9:09 /mile. Slip 10 seconds per kilometre and you arrive 7 minutes late. Bank a minute of speed in the first 5 km and you usually pay it back twice in the last 10.
Most consistent finishers run even or negative splits — pace stays the same or gets faster in the second half. Build that into long runs and tempo sessions.
Critical Speed and Threshold Pace
Beyond the five-zone model, modern endurance research talks about critical speed (CS) — the highest pace you can sustain in true metabolic steady state. Practically, CS sits at the upper end of Z3 / bottom of Z4 for most runners. It's the pace you could hold for roughly 30–60 minutes at race effort, and it's the single most predictive number for endurance performance.
Two practical uses:
- Threshold (tempo) runs are paced at or just below CS. The point is to spend time near the metabolic ceiling without crossing it. Cross too far and the session becomes an interval workout in disguise — fatiguing without the threshold-specific adaptation.
- CS shifts faster than VO₂max. Training improves the pace you can hold at threshold months before it meaningfully moves your max oxygen uptake. That's why a couch-to-10K plan produces big race-time gains without a corresponding jump on a treadmill VO₂ test.
You don't need lab testing to find CS. Run a hard, even-paced 3-km time trial and a hard, even-paced 10-min time trial a week apart; the slope of the two efforts approximates critical speed well enough for programming.
Mapping Pace to Zones
A practical translation for a moderately trained 30-year-old:
| Zone | Effort | Approx. pace difference from 10K race pace | |---|---|---| | Z1 — Recovery | Very easy | +90 to +120 sec/km slower | | Z2 — Endurance | Easy aerobic | +45 to +75 sec/km slower | | Z3 — Aerobic/Tempo | Steady, "comfortably hard" | +5 to +20 sec/km slower | | Z4 — Threshold | Race-pace effort | 5K to 10K pace | | Z5 — Max | All-out | ≤ 5K race pace |
These are starting points. Your own paces will shift as you build fitness — re-check every 6–8 weeks.
A Sample Week
For a runner training 5 hours/week with 10K and half-marathon goals:
- Mon — Rest or 30 min Z1 walk
- Tue — 8 km easy in Z1–Z2
- Wed — Intervals: 4 km warm-up + 5 × 1,000 m at Z4 + 5 min recoveries + cool-down
- Thu — 6 km easy in Z2
- Fri — Rest or strength session
- Sat — Tempo: 3 km easy + 4 km in Z3 + 2 km easy
- Sun — Long run: 12–16 km in Z1–Z2
That distributes effort roughly 80% easy / 20% hard, which is the consensus shape across endurance research.
Yasso 800s — A Famous Marathon Predictor
Coach Bart Yasso popularised a simple marathon predictor: run 10 × 800 m with equal-time recoveries, and the average 800 time in minutes:seconds predicts your marathon time in hours:minutes.
- Average 3:30 per 800 → predicted marathon ≈ 3:30
- Average 4:00 per 800 → predicted marathon ≈ 4:00
It's not laboratory-grade — the workout favours runners with a stronger anaerobic ceiling — but it tracks remarkably well within ±10 minutes for trained marathoners. Use it as a fitness check 4–6 weeks before race day, not as a workout to chase weekly.
Periodising a Race Build
A typical race buildup splits into four phases. The same paces look different in each:
- Base (4–8 weeks): ~85% easy. Almost everything in Z1–Z2. One short tempo or strides per week to keep the high end alive.
- Build (4–6 weeks): Add a structured Z3 tempo and one Z4 interval session per week. Long runs continue to grow in Z2.
- Peak (2–3 weeks): Specific work at goal race pace. Marathoners do long runs with goal-pace blocks; 5K runners sharpen Z4–Z5 intervals.
- Taper (1–3 weeks): Volume drops 30–50%. Intensity is preserved. Easy days stay easy.
Most amateur plans collapse build and peak. Splitting them — staying patient in base — is the largest free upgrade most runners can make.
Long Run Pace
Long runs are about time on feet at easy pace, not about hitting goal race pace. A common rule:
Long run pace ≈ goal marathon pace + 30–90 seconds per km.
Long runs are aerobic base, mitochondrial work, fuel adaptation. Hard long runs steal recovery from your harder workouts and add injury risk. Slow it down.
Pace Adjustments for Real-World Conditions
GPS pace is honest only when conditions are honest. Adjust expectations for:
- Hills. Every ~10 m of elevation gain costs roughly 6–8 seconds. On rolling courses, run by effort, not pace.
- Heat. Above ~20 °C, pace at a given heart rate slows ~2% per 5 °C; humidity compounds it. A 5:00 /km tempo in spring is a 5:10 effort in mid-summer.
- Wind. A 20 km/h headwind can add 10–15 seconds per km at marathon effort. A tailwind gives less back than it takes — courses with both rarely cancel out.
- Altitude. Above ~1,500 m, expect 3–5% slower at 5K pace, climbing roughly 1% per 300 m beyond that.
- GPS drift. Watch pace bounces by ±5–10 sec/km in urban canyons and dense tree cover. Trust the average over a kilometre, not the instant reading.
The rule: set the zone first, accept the pace it produces. Reverse that order on weather days and you race a clock instead of running well.
Common Mistakes
- Easy days too fast. The most common amateur error. Z2 should feel almost lazy.
- Tempo days too short. Z3 work pays off in 20–40 minute sustained efforts, not a half-hearted 10 minutes.
- Intervals with too little recovery. If you can't hit prescribed pace by the third rep, recoveries are too short or the pace is too aggressive.
- Picking marathon pace from Riegel without long-run mileage. The formula is honest — you just have to train for the distance.
- Wearing pacing as identity. Pace is a result; effort is the input. On bad days, hit the zone, accept slower pace.
Frequently Asked Questions
Should I run by pace or by heart rate?
Both. Set the zone (heart rate or perceived effort) for the day, then accept whatever pace it produces. Track pace at the same zone over weeks to measure progress.
What's a good first 5K time?
Highly individual — but a fit recreational runner usually lands somewhere between 22 and 30 minutes. Beginners often clock 30–40 minutes; that is fine and improves quickly with consistent training.
How often should I do speed work?
For most amateurs, 1–2 hard sessions per week. More than that, recovery becomes the bottleneck and injury risk climbs.
Are treadmill paces equivalent to outdoor paces?
Approximately yes, with a small adjustment. Setting the treadmill to a 1% incline generally matches the energy cost of a flat outdoor run, controlling for wind resistance.
Why does my pace drop on hot days?
Heart rate rises 10–20 bpm in hot conditions for the same pace. Hold the zone, accept the slower pace, and hydrate. Pushing to "hit splits" in heat is the fastest way to a bad race.
Does cadence matter, or only pace?
Cadence (steps per minute) is a quality marker, not a pace target. Most efficient distance runners settle between 170 and 185 spm at endurance pace. If yours sits below ~160, raising it gradually with metronome work tends to reduce overstriding and lower impact loads — which usually shows up as fewer niggling injuries, not faster splits on day one.
How do I pick a goal pace for my first marathon?
Use a recent half-marathon time, double it, and add 8–12 minutes as a starting estimate. Confirm in training by running a 32-km long run with a 16-km block at goal pace; if those finishing miles feel sustainable, the goal is realistic. The all-or-nothing 5K-extrapolation from Riegel tends to over-promise for first-time marathoners with limited long-run mileage.
Bottom Line
The runners who improve fastest don't always train hardest — they train most appropriately.
- Find your current pace with our Running Pace Calculator.
- Find your zones with our Heart Rate Zone Calculator.
- Run the easy days easy, the hard days hard.
- Re-test paces every 6–8 weeks and project new race times with Riegel.
Pace tells the watch what to show. Zones tell your body whether the workout is doing its job. Use both.
Health and fitness calculations are estimates only and not medical advice. If you are starting from sedentary, have a cardiac condition, or feel unusual symptoms while running, consult a healthcare provider before pushing into hard zones.