Livewell
What size livewell pump actually keeps fish alive?
Quick answer
Livewell gallons equal length times width times depth in inches, divided by 231, the published cubic inches in a gallon. Turning that volume over every 15 to 20 minutes is convention, separate from filling the well in 2 to 3 minutes, which is why a factory pump runs larger than turnover math alone suggests.
A livewell pump gets sized against two entirely different jobs, and confusing them is the most common reason a livewell either wastes battery or does not keep bait alive. The first job is turnover: replacing the well's oxygen by moving the whole volume through roughly every 15 to 20 minutes, which is boating convention rather than a published standard. The second job is fill rate: getting the well from empty to full in about 2 to 3 minutes so nobody stands at the ramp waiting on the pump. These two requirements call for very different flow rates, and the fill rate almost always wins, which is exactly why a factory pump looks oversized against the turnover math alone.
Measured to the waterline actually filled to rather than the top of the well, the gallon figure below is exact math from a published constant. Everything downstream of it, from turnover time to which stocked pump fits, is either a straightforward calculation from a published flow rate or a boating convention, and each table below says which.
On this page
How many gallons is your livewell?
Livewell volume
Published figuregallons = ( length in inches x width in inches x depth in inches ) / 231 231 is the published number of cubic inches in one US gallon Depth is measured to the waterline the well is actually filled to, not to the top rim of the well
This is exact arithmetic from a published constant, not an estimate, and it is the same formula behind the livewell pump calculator on this site.
Sample wells, from a kayak livewell to a tournament boat
A large 30 by 22 by 16 inch bass boat livewell holds about 46 gallons, more than three times a small 20 by 14 by 12 inch portable well.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Length x width x depth (in) | Volume (gal) |
|---|---|
| 20 x 14 x 12 | 15 |
| 24 x 18 x 15 | 28 |
| 26 x 20 x 16 | 36 |
| 30 x 22 x 16 | 46 |
| 36 x 24 x 18 | 67 |
Each figure is the exact result of length times width times depth divided by 231, rounded to the nearest gallon. Substitute your own well's actual measured dimensions to the waterline you fill to.
Turnover: the requirement most pumps are not actually sized for
Turning the whole volume over every 15 to 20 minutes is the convention that puts oxygen back into the water without churning fish around the well all day. Run against the well sizes above, the required flow rate for turnover alone is modest, which is the first clue that a factory pump is sized for something else.
A 46 gallon well needs only 138 to 276 GPH to turn over completely within 20 to 10 minutes, well under most factory pump ratings.
Rule of thumb Boating and fishing convention rather than a published standard. Taught everywhere, useful, and not a specification. Nothing enforces it and no body publishes it.
| Well volume (gal) | 20 min turnover (GPH) | 15 min turnover (GPH) | 10 min turnover (GPH) |
|---|---|---|---|
| 15 | 45 | 60 | 90 |
| 28 | 84 | 112 | 168 |
| 36 | 108 | 144 | 216 |
| 46 | 138 | 184 | 276 |
| 67 | 201 | 268 | 402 |
Required GPH equals well volume times 60 divided by the turnover minutes. Turning the volume over every 15 to 20 minutes is boating convention, not a published standard, and it is a separate requirement from the fill rate below.
Fill rate is the requirement that actually sizes the pump
Filling the well from empty in roughly 2 to 3 minutes is what most anglers actually judge a pump against at the ramp, and it takes a far larger flow rate than turnover math alone would suggest. This is why a pump such as Rule 603STC livewell pump, 800 GPH straight thru-hull looks oversized against the turnover table above and exactly right against the fill table below.
An 800 GPH pump fills a 46 gallon well in about 3.5 minutes, close to the 2 to 3 minute fill convention that actually decides pump size.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Well volume (gal) | Fill time at 500 GPH | Fill time at 800 GPH | Fill time at 1,200 GPH |
|---|---|---|---|
| 15 | 1.8 min | 1.1 min | 0.8 min |
| 28 | 3.4 min | 2.1 min | 1.4 min |
| 36 | 4.3 min | 2.7 min | 1.8 min |
| 46 | 5.5 min | 3.5 min | 2.3 min |
| 67 | 8.0 min | 5.0 min | 3.4 min |
Fill time equals well volume divided by pump flow rate, converted to minutes. These are exact calculations from each pump's own published GPH figure, not a measurement of a specific installation with real hose runs and fittings.
Real pumps, and the well size each fills in about 2.5 minutes
Stepping up from 500 GPH to 1,200 GPH roughly doubles then triples the well size a pump fills within the 2.5 minute fill convention.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Pump | Published GPH | Well size filled in about 2.5 min (gal) |
|---|---|---|
| Rule 601FC livewell pump, 500 GPH straight seacock | 500 | 21 |
| Rule 603STC livewell pump, 800 GPH straight thru-hull | 800 | 33 |
| SEAFLO 05 Series 800 GPH angled livewell pump | 800 | 33 |
| Attwood Tsunami MK2 aerator pump T1200, 1200 GPH | 1,200 | 50 |
Well size filled equals published GPH times 2.5 minutes divided by 60. Choose the row that comfortably covers your own measured well volume rather than sizing to the smallest pump that technically clears turnover.
Frequently asked questions
How many gallons does my livewell hold?
Multiply the well's length, width and depth in inches, all measured to the waterline you actually fill to rather than the top of the well, then divide by 231, the published number of cubic inches in a US gallon. A well measuring 24 by 18 by 15 inches works out to about 28 gallons using this exact formula.
Why is my factory pump so much bigger than the turnover math suggests?
Turnover, replacing the well's oxygen roughly every 15 to 20 minutes, needs a modest flow rate on most wells. Filling the well from empty in about 2 to 3 minutes needs a far larger one, and factory pumps are sized to satisfy the fill requirement, which is almost always the larger of the two numbers. The pump looks oversized only if turnover is the only requirement being checked.
Is 15 to 20 minute turnover a published standard?
No. Turning a livewell's full volume over every 15 to 20 minutes is boating convention repeated across anglers and tournament circuits, not a figure any standards body tests or publishes. It puts oxygen back into the water without churning fish around excessively, and it is a reasonable planning target rather than a specification with an enforced tolerance.
Why does warm water make livewell aeration harder?
Warm water holds less dissolved oxygen than cold water, so the hottest fishing day is also the day a livewell has the least oxygen available to begin with, regardless of pump size. Pumping in more warm surface water does not solve a shortage the water itself cannot hold, which is why a recirculating kit that cools and re-aerates the well's own water works better on hot days than raw water alone.
Should I measure to the top of the well or the waterline?
Measure to the waterline you actually fill the well to, not the top rim. Most anglers do not fill a livewell completely to its walls, and measuring to the rim overstates the real volume, which throws off both the turnover flow rate and the fill time calculated from it. Measure the well as it is actually run on the water.
Does a bigger pump always keep fish healthier?
Not by itself. A pump sized well past the fill requirement wastes battery and can turn the well over far faster than the 15 to 20 minute convention calls for, without adding an oxygen benefit past that point. A correctly sized pump paired with a timer, so it runs only long enough on each cycle to hit turnover, generally keeps fish healthier than an oversized pump run continuously.
Get the complete rigging shopping list
Every item in the beginner, intermediate and expert rigs for both a boat and a kayak, with running totals, in one printable list. No charge.
One list, no sequence of daily emails, and you can leave at any time.
Researched, not professional advice. This page is compiled from published engineering and regulatory figures, manufacturer specifications and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are boating convention rather than published standards, and they are labelled that way wherever they appear. Marine electrical work is not house wiring. Use tinned, finely stranded marine cable, size it for voltage drop and for the ABYC E-11 ampacity table rather than one or the other, and put overcurrent protection within seven inches of the battery positive terminal, because everything between the post and the fuse is unprotected. A lithium battery needs a charger with a lithium profile. Never load a boat past its capacity plate, and remember that canoes and kayaks carry no federal capacity plate at all, so their stated capacity is the manufacturer own figure. Wear the life jacket, and treat early season water as the hazard it is: cold water immersion takes your breath and then your hands long before it takes your core.