Free swim tools

The swim tool hub for triathletes and swimmers

Free calculators for swim pace, critical swim speed, race splits, readiness, and the pool sessions you're missing. No signup. Built on real swim science, and a worldview pace alone can't give you.

What are ZWIM swim tools?

ZWIM swim tools are free calculators for triathletes and swimmers who want to understand swim pace, critical swim speed (CSS), race splits, open-water readiness, SWOLF, and the cost of missed pool sessions. They help you plan training and racing, while ZWIM's Connected Swim Training explains what pace alone cannot show: the propulsion and consistency behind the numbers.

Swim Pace CalculatorPace per 100m or 100yd from distance and time, plus race splits and CSS.Live Swim Split CalculatorTurn a goal time into even or negative splits you can actually hold.Live Critical Swim Speed (CSS)Estimate threshold pace and training zones from a 400m + 200m test.Live Open-Water Split PredictorSprint, Olympic, 70.3 or Ironman swim splits from pool pace + conditions.Live Missed-Swim CostSee how many sessions pool logistics cost you, and how to rebuild the week.Live Swim Readiness ScoreScore your race-day swim readiness and find your weakest limiter.Live Weekly Frequency OptimizerBuild a realistic swim week for your race, level and pool access.Live SWOLF & EfficiencySWOLF, stroke rate and distance per stroke, and what they can't tell you.Live

Which tool answers your question?

Pace is the scoreboard. These tools show the inputs.

Most swim calculators stop once they give you a number. ZWIM tools go one step further: they show what the number means for your training week, your race prep, and the swim-specific sessions you're missing between pool days.

Pace, CSS, and splits are outcomes. A faster pace can come from fitness, body position, pacing, turns, drafting, a wetsuit, or better propulsion, and pace alone can't tell you which one changed. ZWIM measures the propulsion phase, catch, pull and push, as Propulsive Watts, so you can train one of the missing inputs behind the number. Connected Swim Training is built for the days you can't reach the pool.

What swim calculators can, and cannot, tell you

Swim calculators can estimate pace, training zones, race splits, readiness, and training gaps from the information you give them. They cannot perfectly predict race-day performance or explain every part of your stroke. That's why ZWIM separates outcome metrics like pace from propulsion feedback like Propulsive Watts.

Built for triathletes, swimmers, and coaches

Use these tools whether you're training for a sprint, Olympic, 70.3, Ironman, pool race or open-water event, or simply trying to understand whether your swim training is moving in the right direction. They're built for athletes who want numbers they can use, not just numbers to admire.

Swim terms, defined

Swim pace:the time it takes to cover a fixed distance, usually per 100m or 100yd.
Critical Swim Speed (CSS):an estimated threshold swim pace, calculated from a 400m and a 200m time trial, used to set training zones.
Swim split:your target pace broken across a race distance, evenly or as a negative split.
SWOLF:a swim-efficiency metric that adds the time for a length to the stroke count for it; lower is generally more efficient.
Open-water split:the estimated swim time for an open-water race distance, adjusted for wetsuit, sighting and conditions.
Connected Swim Training:ZWIM's category: swim-specific training with real feedback for the days between pool sessions.
Propulsive Watts:ZWIM's metric for propulsion-phase output during the catch, pull and push of the stroke.

Swim tools FAQ

Which swim calculator should I use first?

Start with the Swim Pace Calculator if you know a distance and time. Use the CSS Calculator if you have 200m and 400m time-trial results. Use the Readiness Score if you're preparing for a triathlon swim.

What is the difference between swim pace and CSS?

Swim pace tells you how fast you swam over a distance. Critical Swim Speed estimates a threshold pace you can use to set training zones.

Can these tools predict my triathlon swim time?

They estimate likely race splits from your inputs, but open-water conditions, sighting, drafting, wetsuit use, pacing and race-day stress can change the result.

What is SWOLF in swimming?

SWOLF is a swim-efficiency score: the time for one length plus the number of strokes for it. A lower SWOLF usually means more efficient swimming, though gliding too long can hurt speed.

Are these calculators free?

Yes. Every tool is free to use, with no signup or account required. The pace, split, CSS, open-water and SWOLF tools work in both meters and yards; the readiness, frequency and missed-swim tools don't need a distance unit.

Are they for triathletes or pool swimmers?

Both. Triathletes use them for race planning, open-water readiness and weekly structure; pool swimmers use them for pace, CSS, splits and efficiency.

Why does ZWIM talk about Propulsive Watts on a calculator page?

Because pace and splits show outcomes. Propulsive Watts is ZWIM's metric for propulsion-phase output during ZWIM sessions, one part of what creates those outcomes.

What is Connected Swim Training?

ZWIM's category: swim-specific training with real feedback for the days between pool sessions, measured in Propulsive Watts.

Go deeper

What is Connected Swim Training? Swim training at home for triathletes Free swim pace calculator

The numbers tell you where you are. ZWIM helps you change them.

Connected Swim Training for home: real Propulsive Watts and a real game, for the days you can't get to the pool.

All figures are estimates for training guidance, not race promises. ZWIM helps you add swim-specific work between pool days, while the pool and open water remain where the full swim comes together.