How to measure your aquarium for a custom lid

Measure the tank you own

A custom aquarium lid is built around your measurements and the production drawings you approve. A manufacturer profile can give you a useful head start, but it cannot replace a tape measure on the exact tank the lid will cover. Tanks from the same product line can vary, equipment can be installed differently, and an unpublished clamp or plastic trim can change where a lid needs to sit.

The goal is not to collect every possible number. It is to establish a few reliable reference measurements, then describe every object that interrupts the lid's path. Work from the physical tank, keep the same front/back orientation throughout, and record each value in one unit system.

Enter each physical measurement exactly as measured. Do not add or subtract clearance or “wiggle room.” Keepr applies the required fit allowance.

Keepr defaults to inches and also supports millimetres. Either works. What matters is that you do not switch between them midway through a measurement set or silently round a converted value.

Measure the line shown in each builder animation. Start your tape or calipers at the animated hook/start surface and stop at the animated end surface, then enter that exact physical measurement. The animation beside a field defines what that field is asking for; do not substitute a nearby dimension or calculate your own allowance.

Exact Keepr lid rendering with a continuous frame bearing on the overflow walls and a locating edge on the water side — The continuous overflow frame keeps a flat lid top, bears on the measured overflow walls, and locates on the water side. The builder preview and production drawing use the same geometry.

Gather your measuring kit

Have the tank and its equipment in their normal operating positions before you begin. A light bracket measured on a workbench may present a different footprint after it is clamped to the glass.

You will want:

A metal tape measure with clear inch or millimetre markings.
A straightedge for checking whether the tape is level across the rim.
Calipers or a reliable glass-thickness gauge, if available.
Painter's tape and a fine marker for marking reference edges.
A phone for top, front and side photographs.
The overflow, light mounts, return lines, cables, feeders and other rim-mounted equipment that will stay on the aquarium.

Before recording anything, choose which side is the front. Mark it on a piece of painter's tape. That small orientation cue prevents a rear-left opening from becoming a rear-right opening when you enter the design.

Start with three tank measurements

The Keepr Lid Builder begins with three numbers measured at the top of the aquarium: outside width, outside front-to-back depth and upright wall-glass thickness. Keep the tape straight and level, and measure the glass rather than the stand or cabinet below it.

1. Outside width

Hook the tape on the outside face of one side wall at the top rim. Pull straight across to the outside face of the opposite wall. This is the full outside width of the upright glass.

Take the measurement near the top, where the lid will sit. Do not copy the nominal tank size from a carton or product listing. If the tank has plastic trim that projects beyond the glass, do not decide on your own which surface controls the fit. Photograph the trim from above and from the side, record both the glass span and the trim span, and confirm the seating arrangement with Keepr before ordering.

Current Keepr Builder animation showing aquarium outside width measured between the left and right outer glass faces — Outside width: outside face to outside face, measured at the top with the tape level.

2. Outside front to back

Hook the tape on the outside face of the front wall and pull it straight to the outside face of the rear wall. Measure at the top rim. Keep the tape parallel to the side walls rather than following a diagonal.

Confirm the front/back label before writing the value down. This orientation will also control how you describe overflows, light mounts, wire passages and feeding access later.

Current Keepr Builder animation showing aquarium front-to-back depth measured between the front and rear outer glass faces — Front to back: outside front-wall face to outside rear-wall face.

3. Upright glass thickness

Measure the exposed top edge of an upright wall pane. Exclude silicone, plastic trim and horizontal Eurobrace glass. Calipers are helpful here because the difference between common glass thicknesses can be hard to judge with a wide tape hook.

If all four upright walls match, one measurement can be applied to the set. If the front, back, left and right panes differ, record each one separately. The builder includes a "My walls aren't all the same" option for this case.

Current Keepr Builder animation showing the thickness of an upright aquarium wall pane — Glass thickness: upright wall glass only, measured at an exposed top edge.

What if you can only measure the inside opening?

Do not enter an inside-opening measurement in an outside-dimension field. The current builder asks for the exact outside dimensions of the upright tank walls, plus the wall-glass thickness. If trim or limited access makes an outside measurement unreliable, photograph the rim and contact Keepr before ordering so we can confirm the correct measurement approach for your tank.

How a Keepr lid sits on the tank

A Keepr lid is not completely flat on the bottom or underside. The upper frame rests on the tank walls or Eurobrace, while a shallow locating edge—sometimes described as an inner lip—sits inside the clear opening to help keep the lid positioned.

That locating edge is part of the finished lid, not an extra measurement for you to calculate. Enter the exact physical dimensions the Keepr Lid Builder requests. Do not enlarge an opening measurement for wiggle room or reduce it to create your own clearance; Keepr applies the required fit allowance when it creates the finished lid.

Identify what supports the lid

The next decision is where the finished lid will rest. On many tanks, the lid caps the upright tank walls. A Eurobrace tank is different: a horizontal glass shelf runs around the inside of the rim, and the lid is seated within the tank walls on that shelf.

For the Eurobrace clear opening and its support shelf, record the same three measurements the Keepr Lid Builder asks for:

Clear opening width between the left and right inner brace edges.
Clear opening front-to-back depth between the front and rear inner brace edges.
Frame overlap on the Eurobrace, measured outward from the clear-opening inner edge to where the finished frame's outside edge should sit on the glass shelf.

Measure both clear spans directly, edge to edge, rather than calculating them from assumed shelf widths. Enter those exact measurements without adding clearance or wiggle room. Frame overlap tells Keepr how much of the finished frame rests on the glass shelf; it is separate from the clear-opening measurement and is not fit clearance. If the opening is visibly different on opposite sides, photograph it and contact Keepr before ordering because the builder calculates a symmetric brace position from the clear opening.

Animated Keepr Builder guide showing clear Eurobrace opening width between the left and right inner brace edges — The Eurobrace animations match the three values entered in the builder: exact clear width, exact clear front-to-back depth and frame overlap on the glass shelf.

Animated Keepr Builder guide showing clear Eurobrace opening depth between the front and rear inner brace edges — The Eurobrace animations match the three values entered in the builder: exact clear width, exact clear front-to-back depth and frame overlap on the glass shelf.

Plastic trim, centre braces, clips, irregular corners, curved fronts and unusual ledges can also affect the seating surface. Do not force these into the tank-wall or Eurobrace instructions if the geometry does not match. Photograph the full rim and the detail in question, include a ruler in the close-up, and ask Keepr to confirm the right measurement path.

Map everything that meets the rim

Now look down at the aquarium as if the lid were already in place. Every object that crosses, clamps to, rests on or rises through that plane needs a route. Measure hardware while it is installed and tightened in the position you intend to keep.

Current Keepr frame surrounding a measured overflow, with mesh and feeding access — Plan overflow walls, equipment openings, water-side cable passages and feeding access around the lid you will review.

Overflow boxes

For an overflow, record the physical wall thickness, outside span, inward reach, position and attached sides using the surfaces shown beside each field. Measure the vertical drop from the glass surface supporting the lid to the top of the overflow wall. Enter 0 when those surfaces are flush. The frame bears on the overflow wall and extends below it on the water side with clearance.

For a Eurobrace tank, measure only the overflow portion exposed inside the brace opening, starting from the inside edge of the eurobrace. Measure the vertical drop from the top of the eurobrace to the exposed overflow wall top. The lid rests on the eurobrace and those exposed walls; covered portions of the overflow need no separate lid support.

If the builder loads an overflow from manufacturer information and identifies it as an estimate, verify it on the tank. Update the width, depth, position and attached sides before approval. Published tank dimensions do not always include enough information to cut a finished opening.

Use the animation shown beside each overflow field as the measurement boundary. For the rear-mounted example below, measure from the exact outside-glass or overflow-wall surface where the animated line begins to the exact surface where it ends. If your overflow touches a different pane or more than one pane, follow the pane-aware animation the builder displays for that installation.

Current Keepr Builder animation showing a rear overflow positioned from the left outside tank-glass corner to the nearest overflow wall — Measure the exact animated line for every overflow field. These are the current rear-pane examples; the builder selects the matching pane-aware versions for your installation.

Current Keepr Builder animation showing the full outside width of a rear overflow between its two outside acrylic wall faces — Measure the exact animated line for every overflow field. These are the current rear-pane examples; the builder selects the matching pane-aware versions for your installation.

Light mounts and rails

First classify how the light is supported:

A hanging light with no rim contact may need no opening, although a suspended rail can still cross the lid.
A clamp or rigid arm needs a cutout around the installed clamp body.
A rail system may have several feet or brackets, including hardware at both the front and rear.
A fixture that rests on the rim needs a supported landing area, not automatically a pocket cut around each foot.

Measure the part the lid must pass around. Manufacturer specifications often publish jaw capacity or arm reach, but those values describe what tank the mount can attach to. They do not establish the clamp body's width along the pane or its inward footprint over the water. Use the installed hardware as the source of truth.

The light-mount animation beside each field defines the two physical surfaces to measure between. Measure the full installed clamp or body shown by the animation; do not enter a manufacturer clearance, jaw capacity or the size of the cutout you think the lid should have.

For repeated mounts, measure each location. If two mounts should remain aligned, verify both offsets from the same tank edge rather than assuming they are mirrored.

Current Keepr Builder animation showing a rear light mount positioned from the left outside tank-glass corner to the nearest outside edge of the clamp body — The builder's light-mount animations measure the installed clamp or body, not the manufacturer's jaw capacity or arm reach.

Current Keepr Builder animation showing the full outside width of a rear light-mount clamp body — The builder's light-mount animations measure the installed clamp or body, not the manufacturer's jaw capacity or arm reach.

Wires, hoses and connectors

A wire passage must clear whatever needs to move through it. If a power plug, controller connector or hose fitting must pass through the finished lid, measure that connector - not only the cable or tube behind it.

Enter the exact diameter of the widest bundle, plug, connector or fitting that must pass through; the builder adds 1 mm total clearance to the finished wire opening. Do not add your own allowance.

Decide whether cables will share a passage or use separate openings. Then check the route from the equipment to the rim, the opening's position along the edge, strain relief, drip loops, and whether the device can be removed for cleaning without dismantling the lid. Leave room for the route you will actually use, not an imagined straight cable that will never move.

Current Keepr Builder animation showing a wire passage positioned from the nearest left physical rim corner to the nearest cable-bundle edge — The builder's wire animations separate where the passage sits from how large it must be.

Current Keepr Builder animation showing the diameter of the widest cable bundle, plug, connector or fitting — The builder's wire animations separate where the passage sits from how large it must be.

Feeding access

Keepr feeding openings are fixed 70 mm square openings placed at an available frame corner. The opening includes a matching feeding lid, and a magnetic feeding cup can be added where available.

Choose a corner you can reach comfortably without moving a light or stretching across the tank. Think about how you feed: pellets, frozen food, a pipette, a feeding ring or a nori tool may each favour a different location. Check that the opening will not compete with an overflow, light cutout, section seam or wire passage.

Other equipment

Walk around the rim once more and look for return lines, dosing tubes, ATO sensors, heater clips, auto-feeders, fans, camera brackets, probe holders, mesh clips and cleaning-tool access. The builder's supported add-ons are overflows, light mounts, wire passages and feeding openings. If another item needs a shape those tools do not represent, contact Keepr before ordering rather than disguising it as the wrong feature.

Design for the work you do every week

A lid can match the tank and still be awkward if daily access is ignored. Before review, picture a water change, glass cleaning, feeding and equipment removal.

Check that:

Each lid section can lift without hitting a light, rail or wall.
The feeding opening is reachable in the tank's normal location.
Cables and hoses can move without rubbing a sharp route or pulling on equipment.
An overflow or light bracket can be serviced without trapping the lid permanently.
Front, back, left and right in the design match the marked orientation on the tank.
Openings do not collide with each other or leave an impractical strip of frame between them.
Future equipment you already expect to add has a deliberate route; hypothetical future hardware should not create oversized gaps today.

The Keepr Lid Builder shows the frame sections, openings and live 3D preview together. Use that preview to inspect the design, then use the production drawings for the final dimensional check.

Measure twice, approve once

Before you approve the drawings, return to the physical tank with your notes. Check every value from the same reference faces used the first time.

Recheck outside width and front-to-back depth at the top rim.
Recheck upright glass and any unequal wall panes.
Recheck the two exact clear-opening spans and frame overlap on the Eurobrace where applicable.
Confirm each overflow's size, position, top drop and attached panes.
Confirm each light mount in its installed orientation.
Confirm wire-passage diameter against the largest item that must pass through.
Confirm feeding access and section removal with the lights in place.
Compare every production drawing with the tank before approving it.

You measure your tank and approve the production drawings. Keepr manufactures to that approved design. Keep the photos and notes until the lid is installed; they are useful if you need to revisit any decision.

The Keepr Fit Guarantee

If it doesn't fit, we'll remake it once at no charge. You pay shipping for the remake.

The Keepr Fit Guarantee applies once per order, to the same tank, when the total dimension change is 2 in or less and the claim is made within 30 days of delivery. Claims are checked against the production drawings you approved.

The guarantee is a backstop, not a substitute for measuring. Careful measurements and a deliberate drawing review remain the best path to a lid built around your tank.

Design your lid

Frequently asked questions

Should I measure the inside or outside of my aquarium?

Measure the exact outside faces of the upright glass and provide the requested wall-glass thicknesses. If you cannot measure the outside reliably, contact Keepr before ordering; do not substitute an inside-opening measurement in an outside-dimension field.

Is the bottom of a Keepr lid flat?

Not completely. The upper frame rests on the tank walls or Eurobrace, while a shallow locating edge, or inner lip, sits inside the clear opening to help keep the lid positioned.

Should I add clearance or wiggle room?

No. Enter each physical measurement exactly as the Keepr Lid Builder requests it. Do not add or subtract your own clearance or wiggle room; Keepr applies the required fit allowance when it creates the finished lid.

Is a manufacturer tank profile enough?

No. A profile is a starting point. Confirm the outside width, front-to-back depth and glass thickness on your tank, then measure every installed opening or mount that the lid must route around.

How do I measure a Eurobrace tank?

Measure the tank's outside dimensions and upright wall glass first. Then measure the exact clear opening width between the left and right inner brace edges, the exact clear opening front-to-back depth between the front and rear inner brace edges, and the frame overlap outward from the clear-opening inner edge to the finished frame's outside edge. Do not add clearance to either clear-opening measurement.

Which part of a light mount should I measure?

Measure the installed body's footprint where it meets the lid plane: its width along the pane, inward reach over the water, position and any repeated feet or rails. Jaw capacity and arm reach do not provide those dimensions.

What if the four tank walls have different glass thicknesses?

Measure and enter the front, back, left and right panes separately. Do not average them. The builder can retain four different wall measurements.

What should I do if my rim or equipment does not match these examples?

Stop before ordering. Photograph the full rim and the unusual detail from above and from the side, include a ruler for scale, and contact Keepr for the correct measurement path.