Gas Strut Force Calculator: What N-Rating Do I Need?

Choosing the wrong gas strut force is the single biggest cause of failed installations. Too weak, and your lid or door won't stay open. Too strong, and it'll shoot up unsafely and damage your hinges.

This guide gives you a simple formula to calculate the correct N-rating for your project, plus a lookup table for the most common UK applications. No engineering degree required.

What Does "N" Mean on a Gas Strut?

The "N" stands for Newtons — the international unit of force. It measures how hard the strut pushes when compressed.

• 60N — Very light lids (small toolboxes, small hatches)
• 100N — Kitchen cabinet doors, small lids
• 150N — Larger cabinet doors, wall units
• 250N — Heavy cabinet doors, small campervan storage
• 400N — Standard automotive bonnets, larger hatches
• 600N–800N — Ottoman bed bases, heavier hatches
• 1000N–1200N — Large ottoman beds, industrial hatches
• 1500N+ — Truck bonnets, industrial equipment

Important: The N-rating is per strut. If you use two struts (which is normal for balanced lifting), the total lifting force is roughly 2x the single-strut rating.

The Simple Formula

For most applications, use this basic calculation:

Weight of lid (kg) × 10 × Safety Factor = Required Force in Newtons (per pair of struts)

Where:

• Weight in kg = the actual weight your struts need to lift
• × 10 = converts kg to Newtons (technically ×9.81, but ×10 is close enough)
• Safety Factor = 1.2 (for balanced applications) to 1.5 (for panels that need to stay firmly open)

Worked Example: Ottoman Bed

• Mattress + bed base = 45kg
• 45kg × 10 = 450N
• 450N × 1.5 (safety factor) = 675N total
• Divided by 2 struts = 338N per strut
• Nearest standard rating: use 350N per strut (or the closest available above this — 400N)

For ottoman beds specifically, most manufacturers oversize this to account for the leverage of the lift mechanism, which is why you commonly see 750N or 1200N ratings.

Worked Example: Kitchen Cabinet Door

• Cupboard door weight = 4kg
• 4kg × 10 = 40N
• 40N × 1.5 = 60N total
• Divided by 2 struts = 30N per strut
• Nearest standard: 50N per strut (small margin above)

For soft-close applications like kitchen cabinets, err slightly higher since the hydraulic damping absorbs some of the force.

Force Rating Lookup Table (Common UK Applications)

Factors That Change the Required Force

The simple formula gets you close, but three factors affect the real answer:

1. Mounting Angle

The steeper the lid opens, the less force is needed to hold it up (gravity does more of the work). If your lid opens past 60°, you can often go one force rating lower.

2. Distance from Hinge

The further the strut is mounted from the hinge, the more leverage it has. Struts mounted close to the hinge need more force to lift the same weight.

3. Opening Speed Preference

If you want a slow, controlled opening (soft-close feel), size slightly under. If you want the lid to shoot open on release, size slightly over.

Signs Your Force Rating Is Wrong

Too weak (needs more force):

• Lid won't stay open on its own
• Lid feels heavy to lift
• Strut extends slowly or partially
• Lid slowly closes over time

Too strong (needs less force):

• Lid shoots open violently
• Hard to close the lid
• Damage to hinges or mounting brackets
• Loud slam when reaching full extension

How to Test Before Buying

If you're unsure, here's a quick test using a bathroom scale:

1. Fully open your existing lid (or the lid you want to fit struts to)
2. Prop it open with something rigid so it stays up
3. Place a bathroom scale under the lid
4. Slowly lower the lid onto the scale until it's holding the full weight
5. Read the weight in kg
6. Apply the formula above

This gives you the exact lift force needed for your specific setup.

FAQs About Gas Strut Force

What's the difference between 100N and 100 Newton? Nothing — they're the same unit. "N" is just the abbreviation for Newtons.

Can I use one strong strut instead of two weaker ones? Not recommended. Two balanced struts prevent twisting, give even lift, and are much safer. If one strut fails, the other holds the lid.

How do I know how heavy my existing lid is? The bathroom scale method above is the most accurate. Or check the manufacturer's specs if you have them.

Can I install struts wrong even with the right N-rating? Yes — mounting distance from the hinge and mounting angle both matter. Follow the manufacturer's guide for your application.

What if my required force is between two standard ratings? Round up. A slightly stronger strut is safer than a slightly weaker one.

Do gas struts weaken over time? Yes — expect about 10–15% force loss over 5 years of typical use. This is normal.

Shop the SpringFix UK Range

We stock gas struts and end fittings across all common force ranges:

• Ottoman Bed Gas Struts → (600N–1200N)
• Kitchen Cabinet Gas Struts → (100N soft-close)
• Toolbox Gas Struts → (60N–140N)
• Gas Strut End Fittings → (ball joints, eyelets, sockets)

Same-day dispatch on all orders placed before 16:00. UK stock, UK dispatched.

Article by SpringFix UK — Your UK source for gas struts, engineering hardware and lift mechanisms.