Calculate Gas Struts: How to Match Newton Force to Cabinet Flap Material

A gas strut holds cabinet doors and lift-up flaps securely open, with the required force in Newtons (N) matched precisely to the weight and height of the respective flap. Anyone planning to build or repair a wall unit often faces the question of how strong the strut needs to be when choosing their fittings. Acting like a perfectly calibrated muscle within the cabinet, this component lifts and supports the front panel. If the force is too low, the door drops down uncontrolled. If it is too high, closing the cabinet requires excessive effort and places undue strain on the hinges.

This guide explains to fitters and experienced tradespeople how to calculate the appropriate values based on material density and dimensions, as well as highlighting key technical criteria for installation.

Key Purchasing Criteria for Flap Fittings

Before installing flap fittings, the physical parameters of the furniture front must be determined precisely. The choice is not made on aesthetics, but on rigorous technical factors.

1. Newton Force (N)

The extension force of a gas strut is specified in Newtons. Standard commercial models for cabinet making range from 50 N to 150 N each. A simplified rule of thumb states that 10 N corresponds to a holding force of approximately 1 kg. However, because the front pivots on hinges, leverage comes into play. Simply converting the weight is therefore not enough; the height of the flap plays an equally important role.

2. Flap Weight and Material Density

The weight of the front is the primary factor in the calculation. It is calculated from the volume of the board (height × width × thickness in m) multiplied by the density of the material. Benchmark values for common board materials (at 19 mm thickness):

• Chipboard (melamine-faced): approx. 12 kg to 14 kg per square metre
• MDF (Medium-Density Fibreboard): approx. 14 kg to 16 kg per square metre
• Solid wood (e.g. oak): approx. 13 kg to 15 kg per square metre

Do not forget to add the weight of the cabinet handle to the board weight. A solid stainless steel bar handle can easily weigh 0.2 kg to 0.5 kg, altering the centre of gravity of the flap considerably.

3. Dimensions and Stroke

The stroke refers to the maximum extension travel of the piston rod in mm. The overall length of the strut (fully extended) on standard kitchen cabinets is typically 250 mm to 270 mm. The stroke determines how wide the flap opens. Standard opening angles are 75°, 90°, or 110°. For an opening angle of 90°, the mounting point geometry must adhere strictly to the manufacturer specifications.

Calculating Newton Force: The Practical Formula

To find the correct gas struts, joiners generally refer to manufacturer charts. If you wish to estimate the value yourself beforehand, you can use the following steps:

1. Determine the weight: Calculate the weight of the front (width × height × thickness × material density + handle weight).
2. Factor in leverage: Multiply the weight in kg by the height of the flap in mm.
3. Apply the constant: Divide the result by the manufacturer model-specific leverage factor (frequently a value around 13.5 for standard mounting positions).

A practical example without complex formulae: An MDF flap measuring 600 mm (width) × 400 mm (height) at 19 mm thickness weighs approximately 4 kg including the handle. With a flap height of 400 mm, technical charts recommend a total force of approx. 100 N to 120 N for this weight. Because flap stays should always be fitted in pairs (left and right) to prevent door warping, you will need two struts rated at 50 N or 60 N each in this case.

Overview of Types and Options

Depending on the application within furniture construction, struts differ in build and load capacity.

• Standard Gas Struts (50 N - 120 N): The classic choice for kitchen wall cabinets, bathroom furniture, or living room sideboards. They are engineered for light to medium-weight fronts made from chipboard or lightweight MDF.
• Heavy-Duty Struts (150 N and above): When installing large, continuous panels above fridges or heavy solid wood flaps, standard models reach their limits. This is where gas struts for heavy flaps are used to withstand the high torque.
• Brand and System Standards: A widespread industry standard for these fittings is the LIFT-O-MAT system. Replacement parts frequently follow the installation dimensions of this type, making replacements much simpler in the event of wear.

Which Strut for Which Application? (Decision Guide)

Selecting the correct rating is a balancing act. Use these benchmarks as a guide when planning your unit (based on dual-sided installation, meaning two struts per flap):

• If the flap is small (e.g. 300 mm height, 500 mm width) and made from lightweight 16 mm chipboard, then select struts rated at 50 N.
• If you are fitting a standard kitchen wall unit (400 mm height, 600 mm width, 19 mm MDF), then opt for models rated at 80 N.
• If you are building a wide living room flap (400 mm height, 900 mm width), then struts with 100 N to 120 N are required.
• If the front is particularly tall or made from dense material (e.g. 500 mm height, 800 mm width, solid wood), then versions rated at 150 N are strictly necessary.

Note on aesthetics: Inside dark cabinet carcases (such as anthracite or Wotan oak), silver fittings can look out of place. In these instances, colour-matched models are worthwhile, whereas classic silver gas struts remain the universal choice.

Installation Advice

Installing gas struts requires precision. A discrepancy of just 2 mm to 3 mm in the drill holes significantly changes the opening angle and closing action.

Required Tools

• Cordless drill/driver
• Cross-head screwdriver (PZ2 or PH2)
• Tape measure and pencil
• Bradawl or 2 mm wood drill bit

Step-by-Step Installation

1. Check hinges: Before the strut is installed, the flap must be attached to the carcase using appropriate concealed cup hinges. For overlay fronts (standard), this is a full overlay setup. Use hinges without an integrated sprung closing mechanism, as these would work against the gas strut.
2. Mark drilling points: Take the exact spacing measurements from the installation instructions. Most carcase mounting plates are fastened using System 32 (32 mm distance from the front edge).
3. Fixing: Use suitable wood screws and furniture screws for a firm hold in timber-based panels. For standard mounting brackets, 4mm wood screws with a length of 15 mm to 17 mm (for 19 mm board thickness) are recommended to avoid piercing through the outer face.
4. Attaching the strut: Most modern struts feature a clip-on mechanism. Simply press the ball socket of the strut onto the fixed mounting brackets until it audibly clicks into place. The thicker section (cylinder) should generally point upwards, with the thinner piston rod pointing downwards. This ensures optimum lubrication of the internal seals.

Frequently Asked Questions (FAQ)

What happens if the gas strut is too strong? The flap will be very difficult to close. In addition, continuous high pressure is exerted on the concealed hinges and fixing screws, which can eventually rip the fittings out of the chipboard.

Can I install just one strut on small flaps? No. It is strongly recommended to always install two struts (left and right). Single-sided installation causes uneven load distribution. Over time, the front will warp and fail to close flush with the carcase.

Are gas struts and soft-close dampers the same thing? No, they operate on completely opposite principles. A gas strut actively pushes a flap upwards and keeps it open. A furniture damper (soft-close), by contrast, cushions the momentum of a closing door to prevent it from slamming shut.

How do I measure the stroke correctly? The stroke is the active travel distance of the piston rod. Measure it by finding the total length of the strut when fully extended and subtracting the length when fully compressed. The difference in mm is the stroke.

Why does a strut lose force after several years? The cylinder contains nitrogen gas under high pressure. Over the years, microscopic wear on the seals can allow minute amounts of gas to escape. This is normal wear and tear. The strut must then be replaced with a component of identical length and Newton rating.

Suitable Products for Your Project

To turn these theoretical calculations into practice, you will find suitable components for professional cabinet making below:

• Gas Struts for Heavy Flaps – For substantial fronts requiring 150 N or more.
• Flap Fittings – The complete range for wall cabinets and chests.
• Wood Screws and Furniture Screws – The correct fixings for a secure hold in MDF and chipboard.
• LIFT-O-MAT – Established system standards for effortless replacement.