Swim lengths calculator · Free · No sign-up
Swim Lengths Calculator
A swim lengths calculator multiplies the lengths you swam by your pool’s length to give the distance, or divides a distance by the pool length to give the lengths. This one takes any pool, holds 33⅓ exactly, gives both the far-end and back-at-the-start counts, and corrects a watch set to the wrong pool.
A mile is 70.4 lengths of a 25-yard pool: 71 to reach it, 72 to finish where you started.
- Metres
- 1,463
- Yards
- 1,600
- Kilometres
- 1.463
- Miles
- 0.909
- Pace per 100 m
- 2:11
- Pace per 100 yd
- 2:00
- Exactly
- 70.4
- To reach it (far end)
- 71
- Back at the start
- 72
- Laps of two lengths
- 35.5
| Distance | Exactly | To reach it | Back at the start |
|---|---|---|---|
| 400 m | 17.5 | 18 | 18 |
| 500 yd | 20 | 20 | 20 |
| 750 m | 32.81 | 33 | 34 |
| 800 m | 35 | 35 | 36 |
| 1,000 m | 43.74 | 44 | 44 |
| 1,500 m | 65.62 | 66 | 66 |
| 1,650 yd | 66 | 66 | 66 |
| 1 mile | 70.4 | 71 | 72 |
| 1.2 mi | 84.48 | 85 | 86 |
| 2,000 m | 87.49 | 88 | 88 |
| 2.4 mi | 168.96 | 169 | 170 |
| 5 km | 218.72 | 219 | 220 |
- Lengths it counted
- 64
- It showed
- 1,600 m
- Real metres
- 1,463
- Real yards
- 1,600
The figures above are an example: replace them with yours. Worked out in this browser and kept there. To count the lengths as you swim them, use the lap counter.
Sixty-four lengths is 1,600 metres in one pool and 1,600 yards in the next, and a watch set to the wrong one is 9% out on every length. Pick the pool, and turn lengths into distance, distance into lengths, or a watch’s figure into the real one.
A length is one swim from one end of the pool to the other. Distance in a pool is the number of lengths times the length of the pool, so the same count is a different distance in every pool: a length of a 25-yard pool is 22.86 metres.
- No sign-up
- Nothing sent anywhere
- Any pool length
- Works offline
- Shows its working
Key facts
| Detail | Answer |
|---|---|
| Price | Free, no sign-up, nothing to install |
| Pools | 25 m, 50 m, 25 yd, 33⅓ m, 33⅓ yd, 20 m, 20 yd, 15 m, or any length in m, yd or ft |
| Lengths to distance | Metres, yards, kilometres and miles, with pace per 100 m and 100 yd from a time |
| Distance to lengths | The exact figure, the fewest lengths to reach it, and the fewest to finish where you started |
| Fix a watch | The distance a watch showed under the wrong pool setting, turned into the real one |
| Lap or length | Count either; a lap is taken as two lengths when you choose laps |
| Exactness | Yard 0.9144 m and mile 1,609.344 m exactly; a third held as a third |
| Where figures are kept | This browser only |
How to work out swim distance from lengths
Pick the pool, then go whichever way you need.
Pick the pool length
Choose a standard pool or Other length and enter yours in metres, yards or feet. Measure wall to wall along the lane at the water line if you are not sure.
Choose what to work out
Lengths to distance after a swim, Distance to lengths before one, or Fix a watch if its figure looks wrong.
Say whether you counted lengths or laps
A length is one way; a lap here is there and back. Most sets and races are written in lengths.
Add the time for a pace
Type it as minutes:seconds. The pace comes per 100 m and per 100 yd.
Decide which end to finish at
For a target distance, the board gives the fewest lengths that reach it; tick the box to make it an even number, back where you started.
Count the swim itself
Tap the lap counter at each wall so the number you enter is the one you swam.
Who needs pool lengths turned into distance
Anyone whose pool is not the one the chart was printed for.
Lap swimmers with a target
A mile, a kilometre or 2,000 m before work: the number of lengths, and whether it leaves you at the far end.
Triathletes
750 m, 1,500 m, 1.2 or 2.4 miles turned into lengths of the pool you train in, yards or metres.
Hotel and home pools
A 15 m hotel pool or a 40-foot backyard pool: any length, in feet if that is how it was sold.
Swim watch owners
A session recorded under the wrong pool size, turned back into the distance you swam.
Coaches writing sets
Lengths for a set in a 33⅓ m or 20 yd pool, without the rounding errors of 33.33.
Sponsored and challenge swims
A charity distance turned into a length count for the lane counter.
How many lengths is a mile? Two answers, and three miles
A mile is 70.4 lengths of a 25-yard pool, and no lifeguard will tell you to swim 70.4. The figure you are given is 70 or 72, and the reason is the wall. An odd number of lengths leaves you at the far end of the pool; an even number brings you back to the end where your bottle and towel are. Round 70.4 down to the even number below and you stop 10 yards short; round it up to the even number above and you swim 40 yards over. U.S. Masters Swimming gives exactly that pair, 70 or 72 in a 25-yard pool and 64 or 66 in a 25-metre pool. Most calculators give one number, and it is usually the quotient.
The calculator above gives all three: the exact quotient, the fewest whole lengths that reach the distance (and which end that leaves you at), and the fewest that also bring you back to the start. Tick “Finish at the end I started from” and the board shows the third.
| Distance | 25 m | 50 m | 25 yd | 33⅓ m | 33⅓ yd | 20 m |
|---|---|---|---|---|---|---|
| 1 mile (1,760 yd) | 64.37 (65 / 66) | 32.19 (33 / 34) | 70.4 (71 / 72) | 48.28 (49 / 50) | 52.8 (53 / 54) | 80.47 (81 / 82) |
| 1,650 yd, the swimmer’s mile | 60.35 (61 / 62) | 30.18 (31 / 32) | 66 (66 / 66) | 45.26 (46 / 46) | 49.5 (50 / 50) | 75.44 (76 / 76) |
| 1,500 m, the metric mile | 60 (60 / 60) | 30 (30 / 30) | 65.62 (66 / 66) | 45 (45 / 46) | 49.21 (50 / 50) | 75 (75 / 76) |
Three distances get called a mile at a pool, and they are not the same swim:
The statute mile, 1,760 yards or 1,609.344 metres exactly, since the yard was fixed at 0.9144 m in 1959.
The 1,650-yard “swimmer’s mile”, the longest freestyle race in short-course yards, which is 66 lengths of a 25-yard pool and, by USMS’s figures, 110 yards (6.25%) short of a true mile.
The 1,500-metre “metric mile”, 109.344 metres (6.8%) short of a mile and about 1,640 yards. It is 8.76 m shorter than the swimmer’s mile, which comes to 1,508.76 m.
Every figure in the table is the distance divided by the pool length, with the length held exactly: a 25-yard length is 22.86 m, and a third is a third. Source for the rounding and the shortfalls: U.S. Masters Swimming, “How Many Laps Make a Mile in Swimming?”, Elaine K. Howley, 5 February 2021, read 26 October 2026.
33⅓ m and 33⅓ yd pools: why 33.33 gives the wrong answer
Some pools are built so that three lengths make a round hundred: 33⅓ metres, three lengths to 100 m, and 33⅓ yards, which is exactly 100 feet (30.48 m). A third has no last digit, so most calculators take a pool length of 33.33 or 33.3 instead, and the small error on every length lands exactly where it does the most harm: on a round distance that should come out whole.
| Distance | A true third | Divided by 33.33 | Divided by 33.3 |
|---|---|---|---|
| 400 m | 12 | 12.0012, rounded up 13 | 12.012, rounded up 13 |
| 1,000 m | 30 | 30.003, rounded up 31 | 30.03, rounded up 31 |
| 1,500 m | 45 | 45.0045, rounded up 46 | 45.045, rounded up 46 |
| What 45 lengths come to | 1,500 m | 1,499.85 m | 1,498.5 m |
A calculator that rounds the lengths up, which is the right way to reach a distance, turns 45.0045 into 46 and sends you a length further than the set asks for. One that reports the distance swum shows 1,499.85 m for a 1,500 m swim. This calculator holds the pool as an exact third, so 45 lengths are 1,500 m and 1,500 m is 45 lengths, finishing at the far end; 46 brings you back.
The yard version works the same way. A 33⅓-yard pool is 3 lengths to 100 yards, 15 to 500 yards, 49.5 to the 1,650-yard swimmer’s mile and 52.8 to a statute mile, because a mile is 5,280 feet and each length is 100. For any other pool, choose “Other length” and enter it in metres, yards or feet: a 40-foot home pool is exactly 132 lengths to the mile.
A swim watch set to the wrong pool: getting the real distance back
A swim watch does not measure distance in a pool. It counts the lengths it detects and multiplies them by the pool size you gave it before the swim; Garmin’s Forerunner 245 manual, “Tips for Swimming Activities” has you “select your pool size or enter a custom size” before starting, and the device then uses that size the next time too. A wrong setting is therefore wrong by the same factor on every length, and it carries over to tomorrow’s swim. The lengths themselves are usually still right, which is what makes the distance recoverable.
| Watch set to | Pool really | The watch reads | Multiply its distance by | Example |
|---|---|---|---|---|
| 25 m | 25 yd | 9.4% high | 0.9144 | 1,600 m shown is 1,463 m, or 1,600 yd |
| 25 yd | 25 m | 8.6% low | 1.0936 | 1,750 yd shown is 1,750 m |
| 25 m | 50 m | Half | 2 | 1,000 m shown is 2,000 m |
| 50 m | 25 m | Double | 0.5 | 2,000 m shown is 1,000 m |
| 33 m | 33⅓ m | 1.0% low | 1.0101 | 1,485 m shown is 1,500 m |
| 25 m | 20 m | 25% high | 0.8 | 2,000 m shown is 1,600 m |
Choose Fix a watch above, set the pool size the watch used and the pool you really swam in, and enter the distance the watch shows in whatever unit it shows it. The calculator divides by the setting to get the lengths back, rounds to a whole length (a watch only ever records whole lengths), and multiplies by the real pool. If the distance is not close to a whole number of lengths of the setting, it says so, because then either the figure or the setting entered is not the one the watch used.
This fixes the multiplication, not the counting. A watch that missed a length in a kick set, or added one when you stopped mid-pool, is wrong in a way no setting explains; the lap counter’s notes on what a swim watch does not count cover that, and a tap at every wall is the check. Some watch apps let you change the pool size of a saved swim afterwards; where yours does, that is the place to correct the record, and this gives you the figure to expect.
Pace per 100 yd and per 100 m are different hundreds
Pace in a pool is given per 100, and the hundred is in the pool’s unit. A hundred yards is 91.44 m, so the same swim is a faster-looking pace in yards: 2:00 per 100 yd is 2:11 per 100 m. Enter the time a swim took and the calculator gives both, worked from the exact distance rather than from rounded lengths.
| Per 100 yd | Per 100 m | A mile at that pace |
|---|---|---|
| 1:20 | 1:27 | 23:28 |
| 1:30 | 1:38 | 26:24 |
| 1:40 | 1:49 | 29:20 |
| 2:00 | 2:11 | 35:12 |
| 2:30 | 2:44 | 44:00 |
| 3:00 | 3:17 | 52:48 |
This converts a pace between units, which is arithmetic. Converting a race time from a yard pool to a metre pool, or from short course to long course, is not: a 25-yard pool has more turns and push-offs per 100 than a 50-metre pool, so the swim itself is different, and swimming bodies publish conversion factors for that. Use those for entry times; use this for “how far, how fast”.
What this calculator does not do
The calculator does distance and pace arithmetic for a pool whose length you know. It does not:
| It does | It does not |
|---|---|
| Turn lengths or laps into metres, yards, kilometres and miles, for any pool length | Count your lengths while you swim: the lap counter does that |
| Give the lengths for a distance, the far end and back at the start | Measure your pool: enter the length you measured or were told |
| Correct a distance a watch multiplied by the wrong pool size | Find lengths a watch missed or added |
| Give pace per 100 m and per 100 yd | Convert race times between pool types |
| Keep your figures in this browser | Estimate open-water distance, which is a GPS question |
Calculator, lengths chart, converter or swim watch
Four ways to turn lengths into distance, and where each one stops.
| This calculator | A lengths chart | A typical lengths converter | A swim watch | |
|---|---|---|---|---|
| Cost | Free, no sign-up | Free | Free | The watch |
| Any pool length | Yes, m, yd or ft | Three or four pools | Usually | Yes, if set before the swim |
| 33⅓ pools held exactly | Yes | Rarely listed | Usually 33.33 or 33.3 | Depends on the custom setting |
| Far end or back at the start | Both shown | One rounded figure | One figure | Not applicable |
| Corrects a wrong pool setting | Yes | No | No | Some apps, afterwards |
| Pace per 100 m and 100 yd | Both | No | Sometimes | In its own unit |
| Account needed | No | No | No | Usually, for the app |
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Frequently asked questions
How many laps is a mile in a 25-yard pool?
A mile is 1,760 yards, so it is 70.4 lengths of a 25-yard pool. Swim 71 to complete it, or 72 to finish at the end you started from, which is 36 laps of two lengths. The 1,650-yard swimmer’s mile is exactly 66 lengths, 110 yards short of a true mile.
How many laps is a mile in a 25-meter pool?
A mile is 1,609.344 metres, which is 64.37 lengths of a 25-metre pool. 64 lengths stop about 9 metres short; 65 reach the mile at the far end, and 66 bring you back to the start. The 1,500-metre metric mile is exactly 60 lengths.
How many lengths of a 50-meter pool equal 1 mile?
32.19 lengths. 32 lengths make 1,600 metres, about 9 metres short of a mile, so swim 33 to complete it, finishing at the far end, or 34 to finish where you started. The 1,500-metre race is 30 lengths of a 50-metre pool.
Is a lap one length or two lengths of the pool?
Both are in use. U.S. Masters Swimming counts a lap as two lengths, there and back, while many swimmers and some watches call each length a lap. Sets and race distances are written in lengths or metres, so count lengths, and choose laps in the calculator only if you counted round trips.
What if the target is not divisible by the pool length?
Then no whole number of lengths lands on it. The calculator gives the exact figure, the fewest lengths that reach the distance, and the fewest that also bring you back to the end you started from. For 1,500 metres in a 25-yard pool that is 65.62, 66 and 66.
Why does my swim watch give me a different distance than I calculated manually?
Either it counted a different number of lengths, or it multiplied them by a different pool size. The second is easy to fix: a watch set to 25 m in a 25-yard pool reads 9.4% high on every length. Enter what it showed and its setting under Fix a watch to get the real distance.
How do I figure out the distance of my home pool?
Measure the lane you swim, wall to wall at the water line, not across the deck or the outside of the coping. Enter it under Other length in metres, yards or feet. A 40-foot pool is 13.33 yards a length, so a mile is exactly 132 lengths.
How many lengths is 1 km?
40 lengths of a 25-metre pool, 20 of a 50-metre pool, 30 of a 33⅓-metre pool and 50 of a 20-metre pool. In a 25-yard pool a kilometre is 43.74 lengths, so 44, which also ends back at the start. A kilometre is 1,093.6 yards.
How many lengths is 1,500 m in a 33 1/3 metre pool?
Exactly 45, finishing at the far end; 46 brings you back to the start. The catch is the arithmetic: a calculator that divides by 33.33 instead of a true third gets 45.0045 and, if it rounds up, says 46. Three lengths of a 33⅓ m pool make 100 m exactly.
What is the swimmer's mile?
The 1,650-yard freestyle, the longest race in short-course yards, which swimmers call the mile. It is 66 lengths of a 25-yard pool and, by U.S. Masters Swimming’s figures, 110 yards or 6.25% short of a true mile. The 1,500 m race is about 1,640 yards, shorter still.
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