Sump Turnover Calculator

Inputs

Enter your sump size and pump details. Choose whether to calculate turnover for the sump only or for the full system volume.

Units

Keep volume and flow in the same unit set.

Turnover basis

Total volume = sump + display.

Desired turnover (per hour)

Common targets are 2–6 per hour.

Sump volume

Working water volume inside the sump.

Display volume (optional)

Used only for total system mode.

Rated pump flow (per hour)

Nameplate flow at low head, if available.

Estimated losses (%)

Fittings, bends, valves, filters, friction.

Vertical head height (m)

Rise from sump waterline to return point.

Pump shutoff head (m, optional)

If unknown, leave blank to skip derating.

Reset Run once to enable CSV/PDF downloads.

Example data table

Sample inputs and expected results, useful for quick validation.

Case	Volume used	Rated flow	Loss	Head	Shutoff	Effective flow	Turnovers/hr
Light setup	80 L	700 L/hr	10%	0.8 m	2.8 m	540 L/hr	6.75
Balanced setup	120 L	1200 L/hr	15%	1.2 m	3.2 m	765 L/hr	6.38
Heavier plumbing	150 L	1400 L/hr	25%	1.6 m	3.0 m	490 L/hr	3.27

Note: Effective flow uses the calculator’s loss and head factors.

Formula used

The calculator estimates effective flow using simple adjustment factors:

Loss factor = 1 − (loss% / 100)
Head factor = max(0.05, 1 − (head / shutoff_head)) (only when shutoff head is provided)
Effective flow = rated_flow × loss factor × head factor
Turnovers per hour = effective_flow / volume_used
Minutes per turnover = 60 × volume_used / effective_flow
Required flow for target = desired_turnover × volume_used

These estimates help with planning. For critical builds, confirm flow using real pump curves and measured return flow.

How to use this calculator

Select liters or gallons, then choose the turnover basis.
Enter sump volume, and optionally display volume.
Enter the rated pump flow per hour from specifications.
Estimate plumbing losses, including filters and fittings.
Enter vertical head height. Add shutoff head if known.
Set your desired turnovers per hour, then calculate.
Download CSV or PDF after you see results.

Notes for garden sump planning

Lower turnover can reduce noise and microbubbles.
Higher turnover can improve filtration and oxygenation.
Use valves wisely; excessive throttling increases losses.
Measure actual return flow when tuning a new setup.

Professional guide

1) Turnover rate definition

Turnover rate is the number of times per hour the selected water volume passes through the return loop. A value of 4 turnovers/hr means a full “volume exchange” every 15 minutes. It is a planning metric for filtration contact time, oxygen transfer, and overall circulation stability. It does not guarantee uniform mixing everywhere, but it is a useful first check.

2) Choose the correct volume basis

Use Sump volume only when you care about sump residence time and bubble control. Use Total system volume when the goal is broader circulation across sump plus display water. Total volume is simply sump volume plus display volume, so even small display additions can change turnover noticeably.

3) Convert nameplate flow to effective flow

Pumps are commonly rated at low head. Real piping adds restrictions from elbows, valves, filters, and smaller diameters. A practical starting range is 10–30% loss, and clogged media can push losses higher over time. The calculator applies a loss factor: effective = rated × (1 − loss%).

4) Account for head height

Vertical lift reduces flow. If you know shutoff head, the calculator derates linearly using 1 − (head ÷ shutoff) with a small minimum limit. Example: 1.2 m head on 3.2 m shutoff gives a head factor near 0.63, so the delivered flow is noticeably lower than the rating.

5) Example sizing decision

With 120 L volume, 1200 L/hr rated flow, 15% losses, 1.2 m head, and 3.2 m shutoff head, effective flow is about 765 L/hr. Turnover is roughly 6.38/hr and one turnover takes about 9.4 minutes. If your target is 4/hr, the required effective flow is 480 L/hr, so the setup meets the target with margin. Many garden sump systems operate comfortably around 2–6/hr; very high turnover can raise noise and microbubbles.

FAQs

1) Should I use sump-only or total system volume?

Use sump-only when tuning sump residence time and bubble control. Use total system volume when you want a broad circulation view across sump plus display water.

2) What loss percentage should I enter?

For short, smooth plumbing, 10–15% is reasonable. Complex returns with elbows, filters, reactors, or small pipe diameters often land in the 20–35% range.

3) I don’t know shutoff head. Can I still calculate?

Yes. Leave shutoff head blank and the calculator will skip head derating. You can still apply a loss percentage to keep results conservative.

4) Is higher turnover always better?

Not always. Very high turnover can increase noise, microbubbles, and filter loading. Aim for stable flow that your overflow, mechanical filtration, and sump baffles can handle.

5) Why does the calculator show “flow needed for target”?

It converts your turnover goal into a required effective flow rate. This helps you pick a pump size or decide whether plumbing changes are needed.

6) How can I verify actual turnover?

Measure return flow with a calibrated container and timer, or use an inline flow meter. Compare measured flow to the volume used to compute real turnovers per hour.

7) What if my turnover is below target?

Reduce restrictions first: clean filters, simplify fittings, or increase pipe diameter. If needed, choose a pump with a higher flow rating at your operating head.