Six free swimming calculators covering pace, efficiency, training zones and calorie burn. All tools work in both metres and yards and require no sign-up.
New to the tools? Start with the swim pace calculator to understand your baseline speed per 100m, then use the critical swim speed calculator to find your training threshold — the swimming equivalent of lactate threshold pace in running.
Understanding swim metrics
Pace per 100m is the standard unit for measuring swimming speed — equivalent to minutes-per-kilometre in running. Elite open-water swimmers hold roughly 1:05–1:15 per 100m; recreational swimmers typically range from 1:45–2:30. Pool lane assignments (slow, medium, fast) are usually set around these ranges.
SWOLF (stroke count + time per length) measures efficiency rather than raw speed. A lower SWOLF score indicates you're covering the same distance with fewer strokes, using energy more efficiently. Improving SWOLF through technique work often improves pace more than simply training harder.
Critical Swim Speed (CSS) is the pace you can theoretically sustain indefinitely — your aerobic threshold. Most swim training programmes structure sessions around CSS: recovery swims at CSS-minus, threshold intervals at CSS, and speed work above CSS. It is calculated from a 400m and 200m time trial.
All swimming tools
6Swim Pace Calculator
Convert a swim time and distance into pace per 100m and per 100yd, plus speed.
Open toolSWOLF Score Calculator
Calculate your SWOLF score — swim efficiency combining stroke count and time per length.
Open toolCritical Swim Speed Calculator
Estimate your Critical Swim Speed (CSS) — your threshold pace — from a 400m and 200m time trial.
Open toolSwim Interval (Send-Off) Calculator
Work out send-off intervals for a swim set from your target pace and rest.
Open toolStroke Rate Calculator
Calculate your stroke rate in strokes per minute from strokes counted over a time.
Open toolSwimming Calorie Calculator
Estimate calories burned swimming, by stroke, intensity, bodyweight and time.
Open toolFrequently asked questions
What is a good swimming pace per 100m?
It depends on stroke and level. For freestyle (front crawl): elite competitive swimmers hold 1:00–1:15 per 100m; strong club swimmers 1:15–1:35; recreational swimmers 1:45–2:30+. Breaststroke is typically 25–40 seconds slower per 100m than freestyle for the same swimmer. If you can hold under 2:00 per 100m in freestyle with good technique, you are swimming at an above-recreational level.
What is SWOLF and why does it matter?
SWOLF is strokes per length + time per length. A swimmer completing a 25m length in 22 seconds taking 16 strokes has a SWOLF of 38. Lower is more efficient. Most fitness trackers calculate SWOLF automatically. Tracking SWOLF helps identify whether fitness gains are coming from improved technique (SWOLF decreasing) or just harder effort (pace faster but SWOLF unchanged).
How do I calculate calories burned swimming?
The most accurate method uses MET (metabolic equivalent) values by stroke and intensity, multiplied by body weight in kg and duration in hours. Freestyle at moderate effort is approximately MET 5.8; vigorous freestyle is MET 9.8; breaststroke is MET 5.3–10.3 depending on intensity. Use the swimming calorie calculator for a quick estimate that accounts for all these variables.
What is Critical Swim Speed?
CSS is your estimated aerobic threshold pace — the fastest pace you can sustain aerobically over an extended swim. It is calculated from the difference between a 400m and 200m time trial: CSS = (400m distance − 200m distance) ÷ (400m time − 200m time). Most structured swim programmes use CSS as the basis for training zone calculation, with the majority of volume done below CSS and threshold sets at or near it.