Turn Efficiency Calculator
The formula
What the turn gain tells you
The flip-turn audit: the 15→15 m zone a video referee watches, compared against swimming the same 30 m through — the number that explains why short course is faster.
Calculation: Gain per turn = 30/swim − t15; glide decay = (push²−breakout²)/2a. Enter your inputs and every substitution is shown below the result.
Reading the result
A turn that merely matches swim-through speed is wasted; the push-off plus streamline must beat the surface pace outright.
Rules of thumb: Club swimmers cross 15→15 in 16–19 s at 1:00/100 pace; sub-elite under 13 s
Limitations and best practice
Glide distance is not free speed: past ~8–10 m the decay eats everything; breakout is a decision, not an accident.
This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Frequently asked questions
Why 15 m either side?
Is turning ever slower than swimming through?
Source & methodology
World Aquatics rule 10.9; turn biomechanics.
Turn Efficiency: the number, the method and the caveats
You are here because you need a specific number, and you want to see how it was produced before you rely on it. Searchers land on a Turn Efficiency page for three reasons — to plan, to compare options, and to check that somebody else’s arithmetic is honest. This tool serves all three, and everything after the calculator explains the model instead of hiding it.
In plain terms, Turn Efficiency answers the question "Gain per turn?". The measurement matters because it converts a situation that feels complicated — several inputs pulling in different directions — into a single number you can act on. Within Fitness & Sports, Swimming is the context where this figure is quoted most often, and professionals treat it as a first-pass screen rather than a verdict.
The number itself is the easy part. What takes judgement is knowing which inputs are facts in your situation and which are guesses wearing a decimal point — a distinction this page makes explicit for every field above.
Nothing below is stock text pasted around a number: the worked example computes gain per turn = 2.18 s from this tool’s own defaults, and the sensitivity section ranks the inputs that move the result — Surface race speed first, at ≈92.6 % of the headline for a ten-percent error either way in that input — which is the thread the rest of this guide pulls on.
Inside the Turn Efficiency calculation: formula and every input
Here is the complete model this tool runs — Gain per turn = 30/swim − t15; glide decay = (push²−breakout²)/2a — with each input explained below. If a competitor’s page gives you a different answer from the same inputs, this is the text that settles which of you is right.
Time 15 m in → 15 m out (s) (example value 16) is a quantity rather than a category — precision here is cheap and worth having. Be precise about the boundary (exact date, start of month); time inputs decide the exponent in most formulas.
Surface race speed (m/s) (example value 2) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Replace the example with the figure from your own records — the tool recomputes instantly and the printed steps follow your numbers.
Push-off speed (m/s) (example value 2) is a measured number in the unit named by the label; the formula does not convert for you. The example value is there to demonstrate the mechanics, not to describe your situation — overwrite it.
Breakout speed (m/s) (example value 2) is a measured number in the unit named by the label; the formula does not convert for you. Replace the example with the figure from your own records — the tool recomputes instantly and the printed steps follow your numbers.
A fully worked Turn Efficiency example
Rather than describe the calculation, here it is end to end — every substitution in order, starting from the inputs above. Starting figures: Time 15 m in → 15 m out (s), Surface race speed (m/s), Push-off speed (m/s), Breakout speed (m/s). The computed gain per turn comes out at 2.18 s, which the interpretation band labels “The wall zone takes 16.0 s against 18.2 s to swim the same 30 m through — 2.2 s gained per turn, which over 30 turns of a short-course 1500 is 65 s, nearly the whole short-course advantage”.
- 30 m at race speed = 30 ÷ 1.65 = 18.18 s
- Actual 15→15 of 16.0 s → 2.2 s per wall
- v²/2a: from 2.4 to 1.7 m/s decays over 1.2 m
Swim-through 30 m — 18.18 s. If your inputs change, this is usually the first companion figure to move.
Glide decay distance — 1.20 m. Read next to the headline, this is the figure that shows the shape of the trade-off.
Gain per 100 m — 4.36 s. This is the number experienced users quote when the headline alone would mislead.
Streamline check — slower breakout than entry = position is the fix. This is the number experienced users quote when the headline alone would mislead.
Keep this worked example open while you enter your own figures: matching the shape of the substitution is the fastest way to spot a unit or convention mistake.
The Turn Efficiency corridor: your result across a realistic band
Single-point answers invite false confidence, so the same engine was run across a band around the input that matters most here. Each row is a full recalculation of Turn Efficiency, not an interpolation.
| Surface race speed setting | Gain per turn |
|---|---|
| 80 % of the example value | 6.73 s |
| 90 % of the example value | 4.20 s |
| example inputs | 2.18 s |
| 110 % of the example value | 0.53 s |
| 120 % of the example value | -0.85 s |
That spread — -0.85 s at the low end, 6.73 s at the high — is what a careful read of Turn Efficiency looks like: a band you can state out loud, with the reason for each edge. Reproduce it in the form above by editing Surface race speed alone; the substitution steps will follow your figures exactly.
Sensitivity: which inputs change Turn Efficiency the most
This list was computed for this specific engine just now: each numeric input was nudged ±10 % while every other field held its example value, and the gain per turn was recalculated from scratch. For Turn Efficiency the ranking is measured rather than guessed, and it belongs to these defaults: shift the starting point and the order can shift with it.
- Surface race speed: ten percent up gives 0.53 s, ten percent down gives 4.20 s — ≈92.6 % of the gain per turn either way
- Time 15 m in → 15 m out: ten percent up gives 0.58 s, ten percent down gives 3.78 s — ≈73.3 % of the gain per turn either way
Surface race speed is the dominant lever here: ten percent either way moves the result by about 92.6 %, from 0.53 s to 4.20 s. That is where a careless figure does the most damage, so check it against a source, and treat Time 15 m in → 15 m out as the second priority (≈73.3 % per ten percent). Everything below that can stay approximate, which is a licence to stop chasing data that would not change the decision.
Reading the result: bands, zones and thresholds
A number on its own is trivia; a number against a range is intelligence. The default case lands in the “The wall zone takes 16.0 s against 18.2 s to swim the same 30 m through — 2.2 s gained per turn, which over 30 turns of a short-course 1500 is 65 s, nearly the whole short-course advantage” band, and bands are deliberately wide because real situations overlap. Before treating the band as fact, note its width: ten percent either way on Surface race speed already spans 0.53 s to 4.20 s. The practical reading rules: ask what would have to change to move you one band. If the answer is “a small, plausible input difference”, the band itself is not the finding — the uncertainty is.
Related measures answer related questions, and the distinctions matter: Turn Efficiency is the quantity, Gain per turn is this tool’s reading of it, and the decision that follows belongs to neither of them separately.
Why Turn Efficiency results go wrong — and how to prevent it
Glide distance is not free speed: past ~8–10 m the decay eats everything; breakout is a decision, not an accident. This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Treating the example inputs as a recommendation. They are a demonstration of the mechanism — a decision-grade Turn Efficiency begins the moment your own figures replace them.
One mistake is specific to this engine: assuming every input matters equally. The computation above shows Surface race speed dominating — a careful figure there beats false precision everywhere else.
The subtlest error is answering the wrong question precisely. Confirm that gain per turn is actually the quantity your decision needs — the arithmetic is flawless either way, which is what makes the mistake invisible.
Six things to confirm before acting on Turn Efficiency
- Note the date and the inputs beside the number so the figure can be audited later.
- Recompute once with the dominant input deliberately set low, and see whether the decision changes.
- Put Surface race speed under a magnifier; the sensitivity table above is the reason why.
- Compare the output against one published benchmark or a colleague’s independent estimate.
- Compare the result with one independent method or published benchmark.
- Run the ±10 % stress on the top two levers and check that your conclusion survives both.
Five steps from raw inputs to a figure you can defend
The tool does the arithmetic; the routine below is what makes the arithmetic trustworthy. Five steps, a minute total — and afterwards you will know not just what the number is, but which assumption produced it.
Step 1 — collect, then type. Everything this tool asks for is listed above (time 15 m in → 15 m out (s), surface race speed (m/s), push-off speed (m/s), breakout speed (m/s)). Pull each figure from something you can point at — paperwork, a dashboard, a label — before touching a field. Guesswork at the input stage cannot be repaired at the interpretation stage. The input you reach for first is usually the one you measured longest ago.
Step 2 — compute the version you would not be embarrassed by. If a stranger audited your inputs, which set would you hand over? Enter that set, read the result, and treat everything else as upside. When in doubt, prefer the boring input: the interesting one is usually the one you misread.
Step 3 — isolate your variables. Change one field, observe, revert. The live sensitivity list does the ranking for the default inputs; verify it against your own, because dominance shifts when the starting point shifts. Most surprises in numbers are surprises about inputs, not about formulas.
Step 4 — stress before you commit. A decision that survives a ten-percent squeeze on its two biggest inputs needs no luck to be sound. One that does not survive is a decision about hope, not about arithmetic. A figure with a date beside it becomes evidence; without one it stays an anecdote.
Step 5 — write the one-line memo. “Gain per turn = 2.18 s on this date, from these inputs.” That line is the entire deliverable; everything else on this page is how you earned the right to write it. Precision is a promise you make about your data; make sure your inputs can keep it.
Who actually uses Turn Efficiency — and when
Most Swimming disagreements are arithmetic disagreements in disguise. When Gain per turn of 2.18 s sits on the table with its working shown, the conversation stops being about who sounds more confident and starts being about which input is wrong. A calculation you cannot explain to somebody else is a calculation you cannot defend.
The companion outputs — Swim-through 30 m and Glide decay distance — exist for the second stage of that screen: the headline sizes the prize, while the companions describe the trade-off you are accepting to get it. When in doubt, prefer the boring input: the interesting one is usually the one you misread.
Treat Turn Efficiency like a smoke alarm rather than a painting — its value is in being tested periodically, not in being admired once. A figure with a date beside it becomes evidence; without one it stays an anecdote.
The questions that come up most about Turn Efficiency
What affects Turn Efficiency the most?
Turn Efficiency is driven above all by Surface race speed. Perturbing only that field by ten percent either way produced 0.53 s against the 2.18 s baseline — a ≈92.6 % response, while Time 15 m in → 15 m out manages ≈73.3 %.
Which matters more: time 15 m in → 15 m out or surface race speed?
By the numbers, Surface race speed: a ten-percent change in it moves the result ≈92.6 %, versus ≈73.3 % for Time 15 m in → 15 m out. Spend your measuring effort in that order — precision on the weaker lever buys almost nothing.
What is a typical Turn Efficiency?
On the worked example above Turn Efficiency comes out at 2.18 s. Treat that as one point on a distribution rather than a norm: the bands, the companion outputs and the sensitivity ranking tell you how wide the plausible range really is.
How do I calculate Turn Efficiency by hand?
Gain per turn = 30/swim − t15; glide decay = (push²−breakout²)/2a is the entire method. Work the inputs in that order — 30 m at race speed = 30 ÷ 1.65 = 18.18 s — and you will reach 2.18 s on the default figures, the same number this tool prints.
What happens to Turn Efficiency if surface race speed changes by 10 %?
Try it in the form above and the printed substitution will follow you; the pre-computed answer for the defaults is 0.53 s to 4.20 s across the ten-percent probe, i.e. ≈92.6 % sensitivity on the gain per turn.
Is the Turn Efficiency result of 2.18 s good or bad?
Neither, on its own — the label “The wall zone takes 16.0 s against 18.2 s to swim the same 30 m through — 2.2 s gained per turn, which over 30 turns of a short-course 1500 is 65 s, nearly the whole short-course advantage” is the band this figure falls in for the example inputs, and your own inputs will place you elsewhere on the same ladder. Judge the number against your history and your alternatives, and remember that a ten-percent error in Surface race speed alone moves it by ≈92.6 %.
What affects Turn Efficiency the most?
Sensitivity depends on where you start, but the inputs Time 15 m in → 15 m out (s) and Surface race speed (m/s) typically move Turn Efficiency further than the rest because they enter the formula multiplicatively. If you can only measure two things well, measure those and hold the others at conservative defaults.
Is Turn Efficiency individualized?
Partly — the tool is mechanical on the inputs you provide (Time 15 m in → 15 m out (s), Surface race speed (m/s)); what varies person-to-person is the response. Start at the computed 2.18 s, adjust by results within a few sessions.
Why 15 m either side?
FINA/World Aquatics rules mark the underwater limit at 15 m, and that’s the protocol’s window.
Is turning ever slower than swimming through?
Yes — a tentative push with a broken streamline gives back the whole advantage and adds 1–2 s.
Does this Turn Efficiency tool store my numbers?
No. The entire calculation runs in your browser session; nothing entered above is transmitted or saved, which is the correct behaviour for sensitive Fitness & Sports figures and the reason you can re-run this page as often as you like.
What the labels on this page mean
- Swim-through 30 m
- 18.18 s on the example inputs — a companion figure printed beside the headline of Turn Efficiency so that no result is read in isolation.
- Glide decay distance
- 1.20 m in the default Turn Efficiency calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Gain per 100 m
- 4.36 s for the Turn Efficiency worked case; it sits next to the main result because it carries context the headline leaves out.
- Gain per turn
- The primary output of this tool: 2.18 s for the default inputs, computed exactly from Gain per turn = 30/swim − t15; glide decay = (push²−breakout²)/2a.
- Worked example
- The calculation written out in full so that nothing on this page has to be taken on trust.
- Verdict band
- The plain-language label — here “The wall zone takes 16.0 s against 18.2 s to swim the same 30 m through — 2.2 s gained per turn, which over 30 turns of a short-course 1500 is 65 s, nearly the whole short-course advantage” — mapping the computed figure onto experience-based ranges for Fitness & Sports.
- Sensitivity (±10 %)
- How far the Turn Efficiency moves when a single input is nudged ten percent either way; the ranked list on this page is computed live from this engine.
The provenance of this Turn Efficiency calculation
The model is published arithmetic implemented exactly as written: Gain per turn = 30/swim − t15; glide decay = (push²−breakout²)/2a. Source of record: World Aquatics rule 10.9; turn biomechanics. Specialist software layers extra coefficients on top of the same algebra; none are hidden here, and that transparency is what makes a disagreement traceable to a specific input instead of a black box.
Nothing here replaces a qualified professional, and nothing here is approximate either — the arithmetic is exact, and the honesty is in the inputs you supply. The promise to the reader is narrow and testable: same inputs, same output, no silent rounding, and no figure presented without the formula that produced it.
After the number: what to do with it
Save the number together with its inputs and today’s date; a Turn Efficiency figure without context is unusable the moment an input changes.
The audience here is people who need one trustworthy number before their next decision. Everything you need to defend the result — formula, substitution, sensitivity, source — is printed above, so the only remaining variable is the honesty of your inputs.