How to Read a Pool Pace Clock (and Build Sets Around It)

The big black-and-red analog clock on the wall of every serious lap pool is the most important piece of equipment after the lane lines. It’s how every structured swim workout in the world communicates — “go 100 on the 1:45” — and once you know how to read it, the entire world of organized swim training opens up.

If you’ve ever felt mystified watching swimmers stare at a wall clock between sets, this article is for you.

What a pace clock is

A pace clock is a large analog clock mounted on the deck or wall of a swimming pool, with a single sweeping second hand (sometimes a separate minute hand). It shows the second going around the face of the clock. The major markings are at the 12, 3, 6, and 9 positions — the “top” (12), the “quarter” (3), the “bottom” (6), and the “three-quarter” (9).

The colors are typically red and black: the red hand sweeps through the first half of the minute (the 12 to the 6), and the black hand sweeps through the second half (the 6 back to the 12). Some clocks use the opposite color scheme, but the pattern is the same — you have an obvious visual cue for what half of the minute you’re in.

Why analog and not digital? Tradition, partly. But also: a sweep hand makes it easy to see “where I’m at” relative to “where I need to be” at a glance, in a way digital readouts don’t.

The basic skill: leaving on an interval

The most fundamental use is leaving on an interval. The coach (or your workout) says: “Swim 100 freestyle, leaving every 2 minutes.”

This means:

• You push off the wall at 0:00 (the top of the minute, on the 12).
• You swim 100 yards.
• You finish — say at 1:25 (one minute, twenty-five seconds after you started).
• You don’t push off again immediately. You wait until the clock reaches 2:00.
• Push off again at 2:00.

The 2:00 is the send-off interval. Your swim time was 1:25. Your rest was 35 seconds (the gap between when you arrived and when you left). The next 100 also starts at the top — but now the clock is on its second cycle, so 2:00 is actually 4:00 on the clock, or 2:00 again if the clock is a single-minute sweep.

This is the core skill. Everything else builds on it.

Reading the clock face

To leave on the 1:45 mark, you need to find 1:45 on the clock face. Here’s how:

• The 12 is :00 (or any whole minute).
• The 3 is :15.
• The 6 is :30.
• The 9 is :45.

So 1:45 means: 1 minute past zero, plus the hand at the 9 position. If you started at 0:00, you push off again when the hand is at the 9 position one full revolution later.

On a single-sweep clock that goes around once per minute, you track minutes by counting cycles or by noting which “color” the hand is on. Many practiced swimmers just remember “left on the 30” (meaning at :30 = the 6 position) and don’t think in absolute minutes.

Send-off intervals in practice

A coach writes a workout like this:

Main set:
6 x 100 free on 1:45
4 x 50 fast on 1:00
200 easy

Reading this:

• 6 x 100 free on 1:45: swim 100 yards, freestyle, six times. Each one starts 1 minute 45 seconds after the previous one started.
• 4 x 50 fast on 1:00: swim 50 yards, fast, four times. Each one starts 1 minute after the previous one.
• 200 easy: swim 200 yards, easy pace, no specific interval.

For the 6 x 100 on 1:45, if you start the first one at the top (12), you push off the next one when the hand returns to the 9 position the next time around. The send-off times are:

The total time for the set is 6 × 1:45 = 10:30 (about 10.5 minutes for the full set).

What “rest” means

The interval is the time between starts, not the time between finishes. So your rest is:

Rest = Interval − Swim time

If you swim a 100 in 1:25 and the interval is 1:45, your rest is 20 seconds.

If you swim a 100 in 1:35 and the interval is 1:45, your rest is 10 seconds.

If you swim a 100 in 1:50 and the interval is 1:45, you’re 5 seconds late — you missed the send-off. The coach will usually either give you a make-up rest (you take a short break before continuing) or adjust the interval for you.

The interval is designed so that:

• Faster swimmers get less rest (the test of fitness)
• Slower swimmers get less rest (so they keep moving)
• All swimmers stay roughly together in the lane

Coaches set intervals to match the lane. The slow lane might do the same set at 2:15 while the fast lane does it at 1:30.

Common interval types

”On the 1:45” or “on a 1:45”

The send-off interval is 1 minute 45 seconds. Standard interval-based swimming.

”Plus 10” or “10 rest”

Swim 100, rest 10 seconds, swim the next 100. Rest is fixed (10 seconds in this case), regardless of how fast you swim. Easier to use without a clock; you just glance up and count to 10.

”1:00 between”

Same idea — fixed rest of 1 minute between repetitions.

”Descending” or “descend”

The interval is the same, but you swim faster each repetition. Example: “5 x 100 on 1:45, descending” means you swim the first one easy, each subsequent one a little faster, and the fifth one is your fastest.

”Negative split”

Within a single repetition, the second half is faster than the first. Example: “100 free, negative split — second 50 faster than the first."

"Build”

Within a single repetition, gradually increase pace from easy to fast. Example: “50 free, build” means you start easy and finish at sprint pace.

Reading the clock when you’re tired

The hardest part of pace clock work is reading it while exhausted. After a few hard 100s, your brain doesn’t want to do math.

Strategies that help:

• Pre-set the send-offs. Before you start the set, write the times on the deck (a few coaches keep markers and a small whiteboard). “1, 1:45, 3:30, 5:15, 7:00, 8:45.” Then you just glance up and find that time.
• Use the position, not the time. Coaches often say “leave on the 30 and the bottom” rather than “leave at 1:30.” The 6 (bottom) is a position; you don’t have to do math.
• Watch a faster swimmer in your lane. If they push off, you push off about 5 seconds later (the standard lane-mate offset). You don’t have to read the clock yourself.

Building your own sets around the clock

Once you understand intervals, you can structure your own workouts. A few approaches:

“T-pace” intervals

Your “threshold pace” (T-pace) is the pace you can sustain for ~30 minutes of continuous swimming. To find it: swim a 1,000-yard time trial. Divide your time by 10 to get your average 100 pace. That’s roughly your T-pace per 100.

Then set intervals based on T-pace plus rest:

• Threshold sets: 10 x 100 on T-pace + 10 seconds. Builds aerobic capacity.
• Endurance sets: 5 x 200 on T-pace + 15 seconds.
• Speed work: 8 x 50 on T-pace per 50 + 20 seconds.

For most adult swimmers, T-pace per 100 is between 1:30 (faster swimmers) and 2:30 (slower). Set your intervals accordingly.

Pyramid sets

Climb up in distance, then back down. Example: “50, 100, 150, 200, 150, 100, 50 — on a base of 1:00 per 50.”

The “base of 1:00 per 50” means each 50 yards gets 1:00 of interval. A 100 is 2:00, a 200 is 4:00, etc.

Negative split sets

The first half of the set is steady, the second half is faster. Example: “8 x 100 on 1:45, first 4 at moderate pace, last 4 fast.”

When you don’t have a pace clock

Many casual lap pools don’t have a pace clock. Options:

• Use your watch. A waterproof sport watch like a Garmin or Suunto has lap timing and interval functions. Push a button at the start, push it again at the wall.
• Use a separate timer. Set a phone timer to beep every 1:45. Push off when it beeps.
• Estimate. For casual fitness swimming, you don’t need exact intervals. “Rest about 20 seconds and go” is fine.

For Masters practice or coached workouts, a real pace clock is the standard. For solo fitness swimming, lower-tech options are fine.

Practical tips for new pace-clock swimmers

• Start in a lane with a clear sightline to the clock. Some lanes have a wall or column blocking the view; pick a lane that doesn’t.
• Memorize the position of common intervals. “1:30 = the 6 = the bottom.” “1:45 = the 9 = the left side.” Pattern recognition is faster than math.
• Ask the coach. If you’re new to a Masters group, the coach will explain the intervals and check on you. That’s part of the job.
• It feels awkward for the first few practices. That’s normal. By the 5th or 6th practice, the clock-reading becomes automatic.

What good clock reading actually feels like

Once you’re fluent: you finish a 100, glance up, see the hand at the 8 position (1:40), know you have 5 seconds until 1:45, take a breath, push off at exactly 1:45.

You don’t think about it. The reading is fast and unconscious. You stay in sync with the lane. The set has structure rather than feeling like random laps.

This is the difference between lap swimming and swim training. The clock is what makes the second thing possible.

For the surrounding swim training context, see masters swimming: how to find your first club and swimming pool etiquette.