# Swimming Pace and Interval Builder Convert swim benchmark times into 25m, 50m, and 100m pacing and generate CSS-style threshold intervals > Canonical page: https://elysiatools.com/en/tools/swimming-pace-interval-builder - **Category:** Health - **Keywords:** swimming, pace, intervals, css, training ## Overview Turns a swim benchmark into split targets and send-off based interval sets so athletes and coaches can build threshold-oriented pool sessions quickly. ## Inputs - **Benchmark Distance** (number) - **Benchmark Time** (number) - **Pool Length** (number) - **Repeats** (number) - **Interval Distance** (number) - **Rest** (number) ## When to use - When planning structured pool workouts based on a recent time trial or benchmark swim. - When calculating exact target splits for 25m, 50m, or 100m intervals to maintain a consistent threshold pace. - When designing send-off times for swim squads or individual training sessions to ensure proper rest ratios. ## How it works - Enter your benchmark swim distance and the time it took to complete it. - Specify your pool length along with your desired interval distance, repeat count, and rest period. - The tool calculates your target split paces and generates a structured interval set with calculated send-off times. ## Use cases - Coaches generating customized send-off times for swim squad lane groups based on varying fitness levels. - Triathletes calculating precise 100m pacing targets for CSS threshold sets in a 25-meter pool. - Fitness swimmers structuring a 10x100m interval workout with consistent rest periods. ## Frequently asked questions ### What is a CSS-style threshold interval? It is a training pace designed to match your Critical Swim Speed, helping improve aerobic capacity by using structured send-off times. ### How does the tool calculate the send-off time? It adds your target interval pace to your desired rest time, rounding to a practical send-off interval. ### Can I use this for both 25m and 50m pools? Yes, you can set the pool length option to either 25 or 50 meters to match your training facility. ### What benchmark distance should I use? Typically, a 100m or 400m time trial benchmark is used to establish baseline threshold paces. ### What does the output JSON contain? It provides calculated split paces (such as pace per 25m) and the final send-off time in seconds for your interval set. ## Related tools - [Sleep Debt Calculator](https://elysiatools.com/en/tools/sleep-debt-calculator): Calculate cumulative sleep debt across the last 7 to 14 nights and generate a gradual recovery plan - [Steady-State Concentration Calculator (Css = F·Dose / CL·τ)](https://elysiatools.com/en/tools/steady-state-concentration): Estimate the average steady-state plasma concentration under repeated fixed-interval dosing: Css,avg = (F · Dose) / (CL · τ), where F is bioavailability (1 for IV, <1 for oral), CL is clearance, and τ is the dosing interval. If t½ and Vd are also provided, computes the one-compartment IV-bolus accumulation index Rac = 1/(1-e^(-kτ)), peak Cmax,ss, trough Cmin,ss, and time to ~94%/~97% of steady state (4/5 half-lives). Valid only for linear pharmacokinetics with fixed dose and interval — NOT for Michaelis-Menten drugs or non-linear kinetics. 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Mode A: given a target peak/trough ratio, solve for the dosing interval τ = ln(P) · t½ / ln2. Mode B: given a chosen interval τ, compute the resulting peak/trough ratio P = e^(kτ). Note: P reflects fluctuation WITHIN one interval and is NOT the accumulation index (R = 1/(1-e^(-kτ))). Valid only for linear one-compartment kinetics, steady state, fixed dose and interval. Not medical advice. - [Elimination Rate Constant Calculator (k = ln2 / t½)](https://elysiatools.com/en/tools/elimination-rate-constant): Convert an elimination half-life to the first-order elimination rate constant: k = ln2 / t½ = 0.693 / t½. Also reports the fraction of drug remaining after 1/2/3/4/5 half-lives (50%, 25%, 12.5%, 6.25%, 3.125%), the number of half-lives required to reach steady state (≈4 for 94%, ≈5 for 97%), and the time to ~99% elimination (≈6.64 half-lives). 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