About

Miscalculating power zones means training at wrong intensities. Ride too hard in recovery and you accumulate fatigue without adaptation. Ride too easy in threshold intervals and you stagnate. This calculator derives zone boundaries from your Functional Threshold Power (FTP), defined as the highest average power you can sustain for approximately 60 min (often estimated from a 20-minute test multiplied by 0.95). Three models are supported: Coggan's classic 7-zone model used in Training and Racing with a Power Meter, British Cycling's 6-zone system, and the Polarized 3-zone model favored in endurance research by Seiler. Each model partitions the power continuum differently based on physiological thresholds.

The tool also computes power-to-weight ratio (W/kg) for each zone boundary when rider mass is provided. This metric determines climbing ability and is the standard comparison unit in professional cycling. Note: FTP drifts with training, illness, and season. Retest every 6 - 8 weeks. The 20-minute protocol overestimates FTP for riders with strong anaerobic capacity. A 40 - 60 minute effort or ramp test may be more accurate for those athletes.

Formulas

Each zone boundary is computed as a percentage of Functional Threshold Power:

P_zone = FTP × %100

Where P_zone is the wattage boundary in W, FTP is Functional Threshold Power in W, and % is the zone-specific percentage from the selected model.

If estimating FTP from a 20-minute test:

FTP = P₂₀ × 0.95

Where P₂₀ is the average power sustained over 20 min. The 0.95 factor accounts for the aerobic decoupling between 20-minute and 60-minute efforts.

Power-to-weight ratio for each zone boundary:

W/kg = P_zonem

Where m is rider mass in kg. A Cat 1 racer typically holds an FTP of 4.5 - 5.5 W/kg. A recreational cyclist is typically 2.0 - 3.0 W/kg.

Reference Data

Zone	Coggan Name	% of FTP	Typical Duration	Physiological Adaptation	RPE (1-10)	Lactate (mmol/L)
1	Active Recovery	< 55%	> 1 hr	Blood flow, glycogen replenishment	2	< 1.0
2	Endurance	56 - 75%	1 - 5 hr	Aerobic base, fat oxidation	3 - 4	1.0 - 2.0
3	Tempo	76 - 90%	1 - 3 hr	Muscular endurance	5 - 6	2.0 - 3.5
4	Lactate Threshold	91 - 105%	10 - 60 min	Lactate clearance, VO₂ improvement	7	3.5 - 5.0
5	VO₂max	106 - 120%	3 - 8 min	Maximal aerobic capacity	8 - 9	5.0 - 8.0
6	Anaerobic Capacity	121 - 150%	30 s - 3 min	Anaerobic glycolysis, lactate tolerance	10	> 8.0
7	Neuromuscular Power	Max	< 30 s	Neuromuscular recruitment, peak power	10	N/A
British Cycling Model
1	Active Recovery	< 60%	Any	Recovery	1 - 2	< 1.0
2	Basic Endurance	60 - 80%	1 - 6 hr	Aerobic base	3 - 4	1.0 - 2.5
3	Intensive Endurance	80 - 90%	30 - 90 min	Tempo / Sweetspot	5 - 6	2.5 - 4.0
4	Threshold	90 - 105%	10 - 40 min	Lactate threshold	7 - 8	4.0 - 6.0
5	VO₂max	105 - 130%	2 - 8 min	Aerobic power	9	> 6.0
6	Anaerobic / Sprint	> 130%	< 2 min	Anaerobic power, neuromuscular	10	N/A
Polarized Model (Seiler)
1	Low Intensity (LIT)	< 80%	1 - 6 hr	Aerobic base (80% of training volume)	1 - 4	< 2.0
2	Threshold (MOD)	80 - 105%	10 - 60 min	Threshold / tempo (minimize time here)	5 - 7	2.0 - 5.0
3	High Intensity (HIT)	> 105%	30 s - 8 min	VO₂max / anaerobic (20% of volume)	8 - 10	> 5.0

Frequently Asked Questions

The 20-minute protocol multiplies average power by 0.95 to approximate 60-minute capacity. This factor assumes a typical aerobic-to-anaerobic ratio. Riders with disproportionately strong anaerobic systems may produce inflated 20-minute numbers, yielding an FTP overestimate of 3-8%. Ramp tests derive FTP as 75% of the last completed stage power and tend to favor riders with high VO₂max but can underestimate FTP for diesel-type athletes with strong fatigue resistance. Neither test is perfect. The gold standard remains a 40-60 minute time trial effort.

Coggan's 7-zone model provides granularity for structured interval prescription. Zones 5, 6, and 7 differentiate VO₂max, anaerobic capacity, and neuromuscular power, each requiring distinct interval durations and recovery protocols. The Polarized model, based on research by Stephen Seiler, simplifies training distribution into low intensity (below ventilatory threshold 1), moderate (between VT1 and VT2), and high intensity (above VT2). The polarized approach prescribes ~80% of training volume in Zone 1 and ~20% in Zone 3, minimizing time in Zone 2. Both models use FTP as a reference but serve different coaching philosophies.

Heat increases cardiac drift and perceived exertion at any given wattage. In temperatures above 30°C, FTP can decline by 5-10% due to thermoregulatory demands redirecting blood flow to the skin. If your FTP was tested in a cool environment (18-22°C) but you train outdoors in summer heat, your effective Zone 4 may feel like Zone 5. Some coaches recommend reducing zone targets by 3-5% per 5°C above the testing temperature. Cold environments below 5°C can also reduce power output due to impaired muscle contractility and vasoconstriction.

FTP approximates the power at which blood lactate reaches a steady state, typically around 4 mmol/L (the onset of blood lactate accumulation, or OBLA). Zone 2 corresponds to powers below the first lactate threshold (LT1, approximately 2 mmol/L), where fat oxidation predominates. Zone 4 straddles LT2 (the second lactate threshold), where lactate production exceeds clearance. Zone 5 and above drive lactate above 6-8 mmol/L. Lab-tested lactate curves provide more precise zone boundaries than percentage-based models because individual lactate kinetics vary. Percentage models assume a population average.

Yes. At altitude, reduced partial pressure of oxygen decreases VO₂max by roughly 6-7% per 1,000 meters above 1,200 m elevation. FTP drops proportionally. At 2,500 m, expect a 10-15% FTP reduction compared to sea level. Zones calculated from a sea-level FTP will be too high for altitude training. Retest FTP at the altitude where you will train, or apply a correction factor: multiply sea-level FTP by (1 − 0.07 × ((altitude − 1200) / 1000)) for altitudes above 1,200 m.

Every 6-8 weeks during a structured training block, or after any significant break (illness, injury, off-season). FTP can change by 5-15 W in a single mesocycle. Training with outdated zones means intervals are either too easy (insufficient stimulus) or too hard (excess fatigue, overtraining risk). Some athletes use rolling 42-day or 90-day power curves from ride data to auto-update FTP estimates without formal testing. This approach requires consistent maximal efforts in training or racing.