How much slower is open water than the pool?

For a swimmer with some open-water racing behind them, coming out of a 25 m pool, this model adds 13 seconds per 100 m before any wetsuit or conditions - 5 for losing the push-offs and 8 for sighting and navigation. A first open-water race is nearer 20 seconds. Rough water or a current can double it.

How much time does a wetsuit save in a triathlon swim?

It depends far more on how well you swim than on the suit. This model saves a strong swimmer about 8 seconds per 100 m, an average one 15, and a weaker one 25. Weaker swimmers gain most because buoyancy fixes body position, and poor body position is usually what is limiting them in the first place.

Why are my pool times so much faster than my race swim?

Three things, and only one is fitness. A 25 m pool gives you a push-off every 25 m, which is worth several seconds per 100. The black line means you never navigate. And a pool is flat, empty and the same temperature throughout. Take those away and the same engine produces a slower pace.

What is Critical Swim Speed and how do I test it?

CSS is the swim equivalent of threshold pace: roughly the pace you could hold indefinitely. Time-trial 400 m, rest until fully recovered, then time-trial 200 m; CSS in seconds per 100 m is the 400 time minus the 200 time, divided by two. It is a much more stable planning number than whatever you swam on any given day.

How much does drafting help in an open-water swim?

Sitting consistently on someone's feet is worth around 7 seconds per 100 m in this model, and occasional drafting about 3. Unlike on the bike, drafting is legal in almost every triathlon swim, which makes it the cheapest time saving in the sport - if you can hold the feet without surging.

Should I use this or my pool time to plan my race?

Use this. A race plan built on pool pace will have you exiting the water minutes ahead of where you actually will, and every downstream number - your bike start, your checkpoint clocks, your cut-off buffer - inherits that error.

Does a downstream swim make my time meaningful?

Not really, and it is worth being honest with yourself about it. Current-assisted swims at races like Chattanooga or Augusta produce times far quicker than the same athlete swims in a lake. Enjoy the split, but do not use it to set expectations for your next race.

Free triathlon planning tool

Triathlon Swim Pace Calculator

Turn the pace you hold in the pool into the pace you will actually swim on race day. It adjusts for the push-offs you lose, the sighting you have to do, the water you are in, and what a wetsuit is really worth to a swimmer of your standard.

Your pool pace (per 100 m)A pace you can repeat across a set, not a single fast 100.

Where that pace came from

Open-water experience

Water state

Current

Wetsuit

Drafting

Race distance

Estimated race swim

37:22

1:58 / 100 m · -2 s vs pool

No walls to push off+5 s

Sighting and navigation+8 s

Wetsuit-15 s

Critical Swim Speed, if you want a better anchor

A single pool pace is whatever you happened to swim that day. CSS is the swim equivalent of threshold: time-trial 400 m, rest until you are fully recovered, then time-trial 200 m. The difference between them, halved, is the pace you could theoretically hold indefinitely - and it is a far more stable number to plan a race from.

400 m time200 m time

Your CSS

1:45 / 100 m

Why pool pace flatters you

“My pool times crash in open water” is one of the most common things triathletes say, and the usual reply is that open water is just harder. That is true but useless: it gives you nothing to plan with. The gap is made of specific, quantifiable things.

In a 25 m pool you push off a wall every 25 metres. Over 1900 m that is 75 push-offs, each giving a few metres of free speed - worth roughly five seconds per 100 m that simply does not exist in a lake. Then there is sighting: lifting your head to navigate breaks your body position every few strokes, and doing it badly means swimming further than the course measures.

Add water that moves, other people to swim around, and a wetsuit you may not have trained in, and the difference between a pool interval and a race split becomes large and predictable. Predictable is the useful part - it means you can plan for it.

Every adjustment this calculator makes

All figures are seconds per 100 m, added to (or subtracted from) your pool pace. They are additive. Published in full because a number you cannot check is not much use for planning a race.

Every adjustment this calculator makes
Factor	Setting	Adjustment
Lost push-offs	From a 25 yd pool	+6 s
Lost push-offs	From a 25 m pool	+5 s
Lost push-offs	From a 50 m pool	+3 s
Lost push-offs	Already open water	0 s
Sighting	Experienced	+4 s
Sighting	Some experience	+8 s
Sighting	First open-water race	+15 s
Water state	Calm	0 s
Water state	Light chop	+6 s
Water state	Rough	+14 s
Current	Downstream / assisted	-12 s
Current	None	0 s
Current	Against	+14 s
Wetsuit	Strong swimmer	-8 s
Wetsuit	Average swimmer	-15 s
Wetsuit	Weaker swimmer	-25 s
Drafting	Occasionally on feet	-3 s
Drafting	Consistently on feet	-7 s

The wetsuit figures reflect what age-group athletes consistently report - roughly 10 s/100 m for strong swimmers and up to 30 for weak ones - rather than a laboratory measurement. The estimate is floored at 80% of your pool pace so that extreme combinations cannot return an impossible time.

The wetsuit question, answered properly

“How much faster am I in a wetsuit?” gets asked constantly and answered with a single number, which is the problem. The honest answer is that it depends almost entirely on how you swim.

A wetsuit lifts your legs. A strong swimmer already has good body position, so there is little to fix and the gain is modest - call it 8 seconds per 100 m, some of which comes back as restricted shoulder movement. A weaker swimmer whose legs sink is carrying enormous drag, and buoyancy removes most of it: 25 seconds per 100 m is realistic, and over an Ironman swim that is more than fifteen minutes.

The practical consequence is about risk, not speed. If you are the swimmer who gains most, you are also the one most exposed by a non-wetsuit call on race morning - and that decision is made on the day, based on water temperature. If your race plan only works in a wetsuit, you do not have a race plan yet.

What to do with the number

Put the adjusted pace, not your pool pace, into the split calculator. Every downstream number inherits this one.
If you are anywhere near a cut-off, check the swim gate with the cutoff calculator using the non-wetsuit figure as your worst case.
Run the estimate twice - once with a wetsuit and once without - so a race-morning announcement is a known quantity rather than a shock.
Practise sighting in a pool by looking forward every six strokes. Most of the sighting penalty is technique, and technique responds quickly.

Frequently asked questions

How much slower is open water than the pool?: For a swimmer with some open-water racing behind them, coming out of a 25 m pool, this model adds 13 seconds per 100 m before any wetsuit or conditions - 5 for losing the push-offs and 8 for sighting and navigation. A first open-water race is nearer 20 seconds. Rough water or a current can double it.
How much time does a wetsuit save in a triathlon swim?: It depends far more on how well you swim than on the suit. This model saves a strong swimmer about 8 seconds per 100 m, an average one 15, and a weaker one 25. Weaker swimmers gain most because buoyancy fixes body position, and poor body position is usually what is limiting them in the first place.
Why are my pool times so much faster than my race swim?: Three things, and only one is fitness. A 25 m pool gives you a push-off every 25 m, which is worth several seconds per 100. The black line means you never navigate. And a pool is flat, empty and the same temperature throughout. Take those away and the same engine produces a slower pace.
What is Critical Swim Speed and how do I test it?: CSS is the swim equivalent of threshold pace: roughly the pace you could hold indefinitely. Time-trial 400 m, rest until fully recovered, then time-trial 200 m; CSS in seconds per 100 m is the 400 time minus the 200 time, divided by two. It is a much more stable planning number than whatever you swam on any given day.
How much does drafting help in an open-water swim?: Sitting consistently on someone's feet is worth around 7 seconds per 100 m in this model, and occasional drafting about 3. Unlike on the bike, drafting is legal in almost every triathlon swim, which makes it the cheapest time saving in the sport - if you can hold the feet without surging.
Should I use this or my pool time to plan my race?: Use this. A race plan built on pool pace will have you exiting the water minutes ahead of where you actually will, and every downstream number - your bike start, your checkpoint clocks, your cut-off buffer - inherits that error.
Does a downstream swim make my time meaningful?: Not really, and it is worth being honest with yourself about it. Current-assisted swims at races like Chattanooga or Augusta produce times far quicker than the same athlete swims in a lake. Enjoy the split, but do not use it to set expectations for your next race.

Related tools and guides

Open-Water Swim Pace Guide

The technique and race-craft side of the same problem.

Triathlon Split Calculator

Feed the adjusted swim pace into a full race plan.

Ironman Cutoff Calculator

Check the swim gate, and what a non-wetsuit swim does to it.

Training Plans

Set your swim zones from the same CSS test.

Ironman Swim Pacing Strategy

How hard to swim when the race is only just starting.

Triathlon Race Predictor

Predict the whole race, swim included, from your test numbers.

Guides that explain this calculator

Open-Water Swim Pace Guide: Convert Pool Pace Into Race Splits

Learn how to estimate open-water swim pace from pool pace, account for sighting and drafting, and avoid over-swimming before the bike.

Ironman Swim Pacing Strategy: Exit the Water Fresh

Master your Ironman 2.4-mile swim with expert pacing strategies. Learn drafting, heart rate zones, and energy conservation to exit the water fresh.

The Science of Triathlon Pacing: Swim, Bike, Run, and Transition Strategy

A practical guide to triathlon pacing physiology — energy systems, fatigue, cardiac drift, and turning calculator splits into race-day execution.

Trust and methodology

How this page should be used

Model last reviewed

August 8, 2026

Maintained by

M Imtinan Farooq

Age-group triathlete and data engineer

Status

Planning estimate, not a race guarantee

Formula summary

Split = distance / pace, converting swim per 100 m or 100 yd, bike speed, and run pace.

Key assumptions

Pace inputs are race-realistic rather than best-ever training numbers.

Limitations

Pace conversion is exact; whether you can hold the pace is the real variable.

Sources

Full formulas, constants, and limitation notes are published on the methodology page. Use the official athlete guide for your own race when it comes to rules, cut-off times, venue policies, and safety instructions - those override anything here.