Interval Timer (HIIT)
General-purpose HIIT interval timer with work seconds, rest seconds, and round-count inputs. Two-tone SVG bar showing alternating red work / green rest segments per round, with a sweep line marking current progress. High-pitched audio beep at work-start (880Hz square wave), lower-pitched beep at rest-start (440Hz), and descending three-note completion fanfare.
Quick Conversion
Formula: total_sec = rounds x (W + R)
Work / Rest Bar
Horizontal bar with red work and emerald rest segments per round. Beeps at every phase change.
Interval Recipes by Sport
Total Workout Duration vs. Round Count
| Work / Rest | 4 rounds | 8 rounds | 12 rounds | 20 rounds |
|---|---|---|---|---|
| 20s / 10s | 02:00 | 04:00 | 06:00 | 10:00 |
| 30s / 15s | 03:00 | 06:00 | 09:00 | 15:00 |
| 30s / 30s | 04:00 | 08:00 | 12:00 | 20:00 |
| 40s / 20s | 04:00 | 08:00 | 12:00 | 20:00 |
| 45s / 15s | 04:00 | 08:00 | 12:00 | 20:00 |
| 60s / 30s | 06:00 | 12:00 | 18:00 | 30:00 |
| 60s / 60s | 08:00 | 16:00 | 24:00 | 40:00 |
| 90s / 30s | 08:00 | 16:00 | 24:00 | 40:00 |
Want the strict Tabata 20/10 x 8 protocol? Tabata Timer >
Interval Math
total_sec = rounds x (work_sec + rest_sec) | work_ratio = work / (work + rest)Worked: 30s work / 15s rest x 12 rounds -> total = 12 x 45 = 540 s = 9 min; work-ratio = 30/45 = 0.667. The Gibala HIIT protocol delivers 6 min of cumulative work in 9 min wall-clock.
The science and history of interval training
In 2026, a CrossFit L2 coach in Boston runs eight different work-rest schemes per class. EMOM, Tabata, Death-by, AMRAP, intervals with descending rest - each demands the timer respond to a different input pattern. This page is the swiss-army knife for that whole coaching workflow: configurable work, configurable rest, configurable rounds, audible beeps, and a visual bar the athletes can glance at without losing rep count.
Interval training dates to the Finnish runner Paavo Nurmi (Olympic champion 1920, 1924, 1928), whose stopwatch-driven 400m repeat sessions on Helsinki cinder tracks set the modern template. The German coach Woldemar Gerschler formalised the system in 1939 with cardiologist Herbert Reindell - their "Freiburger Methode" alternated 200m runs with controlled-recovery walks based on heart rate, the first physiologically-grounded interval protocol.
Emil Zátopek took the method to its limit in the 1948-1956 era, famously running 60 x 400m at 75s with 100m jog recovery as a daily session - winning gold in 5000m, 10000m, and marathon at the 1952 Helsinki Olympics. His training inspired the Hungarian coach Mihaly Igloi who emigrated to the US and trained Jim Beatty and Jim Grelle in the 1960s using 30/30 second on/off repeats.
The modern HIIT revolution arrived in 1996 with Izumi Tabata's Japanese-Olympic-Committee research showing 20/10 x 8 produced VO2max gains equal to 60 minutes of moderate cardio. See the dedicated Tabata Timer for the strict protocol. Veronique Billat (Universite Paris-Sud, 2000) published the 30/30 second protocol for endurance runners - work at vVO2max, rest at 50% - now the standard pre-track-season recipe for middle-distance athletes.
In 2010, Martin Gibala at McMaster University demonstrated that 30/15 x 12 three times a week produced cardiometabolic adaptations matching 5 hours/week of moderate cardio (Gibala et al., The Journal of Physiology, 2010). His "1-minute workout" popularisation (The One-Minute Workout, 2017) made HIIT the dominant fitness modality of the 2020s. The default 30/15 x 12 on this page is the Gibala protocol.
Sprint interval training (SIT) - 8/12 x 30-60 - was developed by Stephen Boutcher (UNSW Sydney) in 2011 and shown to outperform steady-state cardio for fat loss in trained subjects. The metabolic cost is brutal; the protocol is typically reserved for advanced athletes. The SIT preset on this page is one click away.
EMOM (Every Minute On the Minute) originated in CrossFit-style conditioning around 2007 - any movement, start of every minute, rest the remainder of the 60-second window. The 60/0 EMOM preset models this exactly. Combined with our stopwatch for tracking lap splits, you have a complete CrossFit-class toolkit. The Norwegian 4x4 protocol (Helgerud 2007 - 4 min work / 3 min rest x 4) remains the gold-standard cardiac- rehab interval recipe.
How to use the Interval Timer
- Pick a preset or enter custom work seconds, rest seconds, and round count.
- Read the SVG bar to preview the total session - red work + green rest x rounds.
- Press Start. High-pitched beep marks each work-start; lower-pitched beep marks each rest-start.
- Track the sweep line moving across the bar in real time as each round progresses.
- Hear the three-note fanfare when the final round completes. Workout auto-logs to localStorage.
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Trusted by Coaches, Cyclists, Boxers & CrossFitters
“I run 30/30 Billat intervals with my 800m specialists three times a week. The two-tone bar plus the high-pitched work-start beep gives them auditory anchoring at exactly the same instant every rep. Far better than my old phone-stopwatch combo.”
“Standard Crossfit class uses 30 different timers in one hour. This one page replaces my $200 boombox-timer. EMOM 60/0 x 10 with the descending fanfare at completion - the box loves the cue. We programme our daily WOD here.”
“Pro boxing rounds are 3 min work / 1 min rest x 12. The 180/60 preset is exact. Loud beep at bell-start, lower beep at corner-rest. My coaches don't need a separate ring-timer for sparring drills - everyone uses this on their phones.”
“Billat 30/30 intervals before TT season. Power-meter on the bike, this timer on the bars. The work-start beep tells me to hit threshold; the rest beep tells me to spin. Cleaner UI than any cycling-app interval-builder I've used.”
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