What Is Concealed European Hinge Geometry? (Cup Offsets)
A concealed European hinge uses a bored cup in the door and a mounting plate on the cabinet. The cup offset, often called K, measures from the door edge to the nearest edge of the cup bore. Its correct value depends on the hinge model and door layout. Use that model’s template and clearance data; no universal code sets K.
The best-kept secret of a clean hinge installation is that the visible reveal depends on geometry hidden behind the door. A small error in cup position can shift the door, reduce its overlay, or leave too little material at the edge. The remedy is not guesswork or a generic “standard” measurement. It is a checked layout tied to the exact hinge.
I treat the hinge, door, cabinet, and nearby obstacles as one system. The sections below explain how to read cup offset, check clearances, drill safely, and confirm the finished movement.
Planning the Hinge Model and Cup Offset
Cup offset is the distance from the door edge to the nearest edge of the hinge-cup bore. Many catalogs call it K. It is not the distance to the center of the bore. Confirm how the hinge maker defines K, then use that model’s drilling template and adjustment schedule.
A common European concealed hinge uses a 35 mm cup, but cup size and drilling details vary by model. For a 35 mm bore, the radius is 17.5 mm. If K is measured to the bore edge, the bore-center setback is:
Bore-center setback = 17.5 mm + K
| K, edge to bore edge | Bore-center setback for a 35 mm cup | Practical note |
|---|---|---|
| 3 mm | 20.5 mm | Common catalog value; verify the hinge drawing |
| 4 mm | 21.5 mm | Do not assume it suits every door or hinge |
| 5 mm | 22.5 mm | Check edge margin and the model’s template |
| 6 mm | 23.5 mm | A larger K moves the bore farther from the edge |
These values show the geometry, not a universal drilling prescription. Catalog options often fall around 3 to 6 mm, but the hinge’s own specification controls. Do not copy K from a different hinge, even if both hinges have 35 mm cups. A different cup, crank, or drilling pattern can change the required layout.
Also record door thickness, edge shape, cup depth, and the fixing-hole pattern. A square door edge is the simplest case. A bevel, thick edge band, routed profile, or narrow stile can change the safe area available for the bore.
Checking Door, Cabinet, and Opening Clearances
A correct cup location does not by itself set overlay or guarantee that a door will clear nearby parts. Overlay, inset, hinge crank, mounting-plate position, and cabinet geometry work together. Check the hinge maker’s application chart for the selected door and cabinet before drilling.
Overlay describes how far a door covers the cabinet side or front edge when closed. In an inset layout, the door sits within the opening. The hinge’s crank and the mounting plate help set the door’s position, but the result depends on the exact hinge model and plate combination.
Before cutting, survey the whole opening:
- Identify the hinge model and its compatible mounting plate.
- Measure door thickness and the intended overlay or inset.
- Note the cabinet-side thickness and the front edge position.
- Check the door edge profile and any nearby doors, walls, pulls, or appliances.
- Find the manufacturer’s cup-offset, bore-depth, plate-position, and adjustment data.
- Check the model’s stated opening angle and clearance guidance.
Use the manufacturer’s chart or calculator where available. Do not try to derive a universal overlay from K alone. If doors meet at a corner, sit beside a wall, or open near a handle or appliance, check the full swing path. A full-size template or test piece can reveal a collision that a closed-door measurement will miss.
EN 15570 and ANSI/BHMA A156.9 are performance standards for hinges. They address matters such as performance and durability; they do not prescribe one cup offset, overlay, or door-to-cabinet clearance for every installation. Follow the hinge maker’s instructions and applicable project requirements.
Drilling the Cup and Installing the Hardware
The safest drilling sequence starts with a verified layout and ends with a test fit. Set the bit depth before boring, hold the drill square to the door face, and use the specified fixing-hole pattern. Never rely on a generic depth or enlarge holes to make mismatched hardware fit.
Many 35 mm hinges use a cup depth around 12 to 13 mm, but the model’s stated maximum is the limit to follow. In an 18 mm door, a 13 mm bore would leave 5 mm of nominal material. That simple subtraction does not account for veneer, machining variation, or the shape of the cup, so it is not proof that the door is safe to bore.
A careful workflow is:
- Mark the reference edge. Use the door edge specified by the template, and keep the layout square to the face.
- Set K from the bore edge. If the template gives the centerline instead, follow that dimension rather than converting it twice.
- Set a depth stop. Match the hinge specification and test the setting on scrap of similar thickness.
- Bore square to the face. Keep the bit from wandering and stop at the set depth.
- Drill fixing holes to the supplied pattern. Use the specified bit and fastener type.
- Install cup and plate without force. Misaligned screws or hardware can damage the door or weaken the attachment.
Thin or profiled doors need extra care. A cup can break through a veneer, routed panel, or narrow stile even when the nominal door thickness seems adequate. Check the door maker’s minimum remaining material and the hinge cup profile before drilling. If the safe margin is unclear, ask the door or hinge maker rather than testing the finished door.
Verifying Reveals, Travel, and Fastening
After mounting, verify the door in both closed and open positions. Check the reveal, edge clearance, cup seating, and screw engagement, then cycle the door through its full travel. Make only adjustments allowed by the hinge. A sound fit should not depend on forcing parts or stretching the adjustment range.
Start with the door supported so its weight does not twist the hinge during installation. Fit the hinge to the cup and attach the mounting plate using the specified screws. Hang the door, then make small adjustments within the manufacturer’s stated range.
Check for:
- Even gaps around the door and between paired doors.
- No edge binding against the cabinet, adjacent door, wall, pull, or appliance.
- A cup that sits flush and does not break through the face.
- Secure screw engagement in both the door and cabinet.
- Smooth movement through the hinge’s stated travel.
If the reveal cannot be corrected within the hinge’s adjustment range, stop and recheck the layout, plate position, and hinge selection. Do not slot or enlarge holes as a shortcut. That can hide a layout error while reducing the reliability of the fastening.
Worked Installation Scenarios
These examples show how the geometry guides decisions; they are not universal hinge prescriptions. In each case, the hinge maker’s drawing remains the authority. The point is to catch errors before production drilling, especially when door thickness, edge shape, or nearby obstructions limit the available adjustment.
Scenario 1: Standard 18 mm flat door. The selected hinge drawing calls for a 35 mm cup and K of 4 mm. The bore center is therefore 21.5 mm from the edge. The installer confirms the specified depth, uses a depth stop, and tests the cup on scrap before drilling the finished door.
Scenario 2: Narrow stile with a routed profile. The door is thick enough to seem suitable at first glance, but the routed area leaves less material behind the cup than the flat section. The installer checks the door maker’s minimum remaining material and the hinge cup profile. If the cup would intersect the profile or leave an unsafe face, the hinge or door layout must change.
Scenario 3: Door beside a wall. The cup and plate dimensions match the hinge sheet, but the door edge approaches a wall during opening. The installer checks the hinge’s application data and tests the swing with a full-size layout or sample. If the door binds, changing K alone may not solve it; hinge type, plate, door position, or opening angle may need review.
Conclusion: Use the Hinge Drawing, Not a Generic Number
Cup offset is a precise edge-to-bore measurement, but it is only one part of concealed hinge geometry. The selected hinge, plate, door, and cabinet determine the finished position and movement. Confirm the model-specific layout, protect the door’s remaining material, and test the full opening path before repeating the drilling pattern.
For a 35 mm cup, convert K to the centerline only when needed: add 17.5 mm to the edge-based K value. Then verify the actual template, bore depth, fixing pattern, and clearance data. This simple discipline prevents a common error: treating a familiar-looking hinge as if it shared another model’s geometry.
FAQ: Concealed Hinge Cup Offsets
What does K mean on a concealed hinge?
K usually means the distance from the door edge to the nearest edge of the cup bore. Confirm the definition on the specific hinge drawing.
Is K the distance from the door edge to the bore center?
No, not when the catalog defines K as edge-to-bore-edge distance. For a 35 mm cup, add 17.5 mm to K to find the center setback.
What is a common K dimension?
Many catalogs offer values around 3 to 6 mm. The correct value depends on the hinge and door layout, so use the model’s technical sheet.
What is the center setback for a 35 mm cup with K = 5 mm?
It is 22.5 mm from the door edge: 17.5 mm cup radius plus 5 mm K.
Is a 35 mm cup standard for every European hinge?
It is common, but not universal. Confirm the cup diameter and drilling pattern for the exact hinge before boring.
How deep should I drill the cup?
Follow the hinge maker’s specified depth and maximum. Some 35 mm hinges call for roughly 12 to 13 mm, but that range is not a substitute for the model’s instructions.
Do building codes set a universal cup offset?
No universal building-code K dimension applies to all concealed hinges. EN 15570 and ANSI/BHMA A156.9 address hinge performance, not one universal cup layout.
Can I use the same K for a different hinge with a 35 mm cup?
Not safely by assumption. The crank, cup profile, plate, and drilling pattern may differ even when cup diameter matches.
What should I do if the door is thin or profiled?
Check the cup profile and the door maker’s minimum remaining material. A nominal depth calculation alone cannot confirm that the face will not break through.
Can hinge adjustment fix a misplaced cup?
Only within the hinge’s stated adjustment range. If the door cannot be aligned within that range, recheck the layout and hardware rather than enlarging holes.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
