FTP Test Explained: How to Find Your Threshold Power for Triathlon

Functional threshold power (FTP) is the power, in watts, that you can hold for roughly an hour of hard cycling. It's the single most useful number in power-based bike training because almost everything else — your training zones, your workout targets, your race pacing — is expressed as a percentage of it.

But it's just as important to be clear about what FTP isn't. It is a practical estimate, not a directly measured physiological threshold, and research comparing field-test FTP with laboratory threshold measures shows they shouldn't be treated as interchangeable. How long you can actually hold your "FTP" varies from person to person, and the number moves with your pacing, the protocol and even the day.

So treat FTP as a working anchor that starts a training conversation, not a verdict on your worth or a figure to force every session and race to obey. If you're new to power altogether, read cycling watts explained first for what power actually measures — this page is about finding and using your threshold number.

For a triathlete, FTP earns its keep in two places:

• It sets your training zones. Once you have an FTP, your easy, tempo, threshold and harder efforts all fall out of it as power ranges — so your sessions have concrete, repeatable targets instead of vague "ride hard" instructions. How those zones translate into actual workouts is the job of threshold vs sweet-spot training.
• It helps you pace the bike so you can run. The classic triathlon mistake is riding the bike too hard and destroying the run. Knowing your threshold lets you hold a sensible, sub-threshold percentage on the bike and arrive at T2 able to run — which is what pacing strategy and the broader bike-training design are built around.

Keep it in perspective, though: FTP is one useful input, not the whole picture. Consistency, easy volume, durability and fuelling matter more than chasing a bigger threshold number — the point of testing is better decisions, not a trophy.

An FTP test measures power, so you need a device that reports it: a power meter on the bike (crank, pedals or hub) or a smart trainer that measures power indoors. If you're deciding whether that's a worthwhile purchase, power meters for triathlon covers what they do and whether you need one.

No power meter? You can still train effectively. Heart rate and perceived effort organise training well for most age-groupers — see heart-rate zones explained — they just respond more slowly and drift with heat and fatigue, so they pace differently from power. And if you want a more physiological picture than a field test gives, lactate threshold testing at home is a different (and more involved) approach.

Whatever the source, use the same one when you compare results over time. A number from your pedals and a number from a trainer aren't the same measurement.

There's no single "correct" FTP test — several protocols estimate the same number in different ways, each with its own assumptions:

• Ramp test — power steps up steadily until you can't continue; software estimates FTP from your final effort. Short and repeatable, but the estimate can suit some riders better than others.
• 20-minute test — one long, evenly paced maximal effort; FTP is estimated as about 95% of your average (more on the maths below). The most common field test.
• 8-minute test — a shorter effort (often two of them) for athletes who struggle to pace a full 20 minutes; it uses different maths.
• Longer efforts or platform estimates — a full ~60-minute test, or a modelled estimate from your recent rides on a training platform.

The golden rule: don't compare results across protocols or platforms as if the difference must be a fitness change. Pick one method you can repeat, follow its complete protocol (warm-up, effort and cool-down included), and stick with it for tracking. The comparison table below summarises the trade-offs.

The 20-minute test is the most common, so here's how to give it a fair shot:

• Warm up thoroughly — 15–20 minutes with a few short openers so the first minutes of the test aren't wasted easing in.
• Pace it evenly. The classic error is starting too hard and fading; aim for a hard but sustainable effort you could just about hold to the end, and keep it steady. A big negative split usually means you left time on the table with a timid start.
• Choose a controlled setting. Indoors on a trainer removes traffic, junctions and descents; outdoors needs a long, uninterrupted, safe stretch. Never do a maximal effort somewhere handling hazards can bite.
• Be honest about readiness. A maximal test is inappropriate when you're ill, injured, very fatigued or not prepared for hard exercise, and any concerning symptoms during exertion mean stop and seek appropriate medical advice.

A good test is a repeatable one — same protocol, similar conditions — because the goal is a number you can trust and compare to later, not a one-off hero effort.

For the 20-minute test, the convention is:

FTP ≈ average power for the 20 minutes × 0.95

So if you average 240 W across the 20 minutes, your estimated FTP is 240 × 0.95 = 228 W. The ~5% reduction is a rough allowance for the fact that you can hold 20 minutes at a higher power than you could hold for a full hour. Treat 0.95 as a useful convention, not a law — it fits some riders better than others.

Two details that trip people up:

• Use the right input. It is the average power for the defined 20-minute interval — not peak power, not normalized power, and not the average of your whole ride including warm-up.
• Power-to-weight (W/kg) is an FTP estimate divided by body mass: 228 ÷ 75 kg ≈ 3.04 W/kg. This is arithmetic, not a grade of ability. Effort duration, test method and course matter; the triathlon power-to-weight guide explains how to interpret the ratio.

The FTP calculator does this arithmetic for you — but remember it can only do the sum; it cannot tell whether your test was well paced or your meter was calibrated. A ramp or 8-minute test uses different maths, so always label which protocol produced a number.

The payoff for testing is a set of training zones: percentage bands of FTP that give each session a concrete target. Roughly, easy/endurance work sits well below FTP, tempo and sweet-spot just under it, threshold work around it, and VO2/anaerobic efforts above — though the exact boundaries differ between zone systems.

Two honest cautions:

• Zones are organisational ranges, not sharp biological walls. Nothing magic happens at 76% versus 75%. They're a tool for structuring effort, so don't agonise over a single watt.
• Label which system you're using. "Zone 2" or "sweet spot" means different things in different models, so a number is only useful alongside its definition.

The training-zone calculator will lay out bands from your FTP, and threshold vs sweet-spot training explains what to actually do in the most useful ones. Setting zones is where FTP stops being a test score and becomes a training tool.

If you want an FTP number you can track, you have to control the things that quietly change it:

• Same power source, calibrated. Follow the zero-offset/calibration steps, and don't switch power meters and test protocols at the same time — you won't know which caused the change.
• Note the conditions. Indoor vs outdoor, cooling (a fan matters a lot indoors), heat, fatigue, motivation and pacing all move the result. A hot, un-cooled indoor test can read low for reasons that have nothing to do with fitness.
• Sanity-check surprising results. Before you re-zone your whole training around a shock number, inspect the file for dropouts, a wrong interval selection or a sensor glitch.

And resist the temptation to "fix" a disappointing test by quietly applying a friendlier multiplier until the number you wanted appears. That's measuring your hopes, not your threshold.

A test result is a hypothesis; your training confirms or corrects it. Use a new FTP conservatively at first and watch how the sessions feel:

• If work that should be manageable at your zones repeatedly feels unsustainable, your FTP is probably set too high (or you're fatigued) — adjust it down rather than grinding yourself into a hole.
• If everything feels far too easy, the estimate may be low, or your test was under-paced.

Let perceived effort and recovery be part of the verdict, not just the watts. And don't force a long-race power target from a single short test — a full-distance bike is ridden well below threshold, and duration, position, terrain, heat, fuelling and the run afterward all change the right number. FTP informs race pacing; it doesn't dictate it. The pacing framework and data-driven training cover how to hold that perspective.

Retest when a decision needs it — after a solid training block, a clear change in fitness, or an equipment change that requires a fresh baseline. Testing constantly is counter-productive: a maximal effort costs recovery, and week-to-week noise will have you chasing numbers rather than training.

When you do retest, keep the old result, protocol and conditions rather than overwriting them. A short log — date, protocol, warm-up, power source, indoor/outdoor, cooling, recent fatigue, plus both the raw average and the calculated FTP — lets you tell a real trend from one unusually good or bad day, and stops an "improvement" that's really just a changed method from fooling you.

Your next step after a test is always a sensible training adjustment, not a bigger number at any cost. If your FTP supports repeatable sessions and pacing that sets up a good run, it's doing its job — however modest it looks.

FTP is the practical anchor of power-based cycling: the roughly one-hour power that sets your zones and helps you pace the bike so you can run. Find it with a protocol you can repeat — most often a well-paced 20-minute test, estimated at about 95% of your average — record the method alongside the number, and turn it into zones you actually use.

Then hold it lightly. It's an estimate that depends on the protocol, your pacing and the day, so let real training confirm it, retest only when a decision needs it, and never chase a bigger number for its own sake.

Where to go next: cycling watts explained for the fundamentals, threshold vs sweet-spot training for what to do with your zones, heart-rate zones if you train without power, and training basics for how it all fits into a plan.