How do you calculate gas strut force?

Calculate the gravity moment (weight × CG distance × cos(angle)) and divide by the perpendicular distance from the hinge to the strut's line of action. Then divide by the number of struts and multiply by a safety factor of 1.2x. For example, a 15 kg lid with CG at 250 mm from the hinge: Force = (15 × 9.81 × 0.25) / (perpendicular distance × number of struts).

How do you calculate gas strut position?

The strut mount on the lid should be 15-25% of the lid length from the hinge for a balanced feel. The frame mount should be directly below the hinge, typically 30-80 mm away. Mounting closer to the hinge requires higher force but gives smoother control. Mounting further away reduces required force but may cause the lid to swing open too fast.

How do I calculate gas strut size?

Gas strut size has two components: force (in Newtons) and length. Calculate the required force using the torque balance method. For length, measure the distance between mount points when the lid is closed (compressed length) and fully open (extended length). The stroke is the difference between these two lengths. Standard struts have a compressed-to-extended ratio of approximately 60%.

How many gas struts do I need?

Most applications use 2 gas struts (one on each side) for balanced lifting and to prevent the lid from twisting. Use 1 strut only for narrow, lightweight lids under 5 kg. Heavy-duty applications like truck canopies or large hatches may need 4 struts. Using 2 struts halves the required force per strut compared to using just 1.

What force gas strut do I need for a toolbox lid?

For a typical toolbox lid weighing 5-15 kg, you'll need gas struts rated between 80-250 N each (with 2 struts). Calculate precisely: multiply the lid weight by 9.81, then by the CG distance, and divide by the strut mount distance and number of struts. Add a 20% safety factor. A 10 kg toolbox lid with 2 struts typically needs around 100-150 N per strut.

How do gas struts work?

Gas struts contain pressurized nitrogen gas (100-200 bar) inside a sealed cylinder with a piston rod. When compressed, the gas pressure pushes the piston rod outward, creating a lifting force. The force is proportional to the gas pressure and the rod cross-sectional area. An oil damper inside controls the speed of extension, preventing the lid from slamming open.

What is the difference between gas strut force when extended vs compressed?

Gas strut force increases by approximately 10-30% when compressed compared to the extended position. This is because the piston rod displaces internal volume when pushed in, increasing the gas pressure. A strut rated at 200 N (extended) may exert 220-260 N when fully compressed. Force ratings on gas struts refer to the extended (lowest) force.

Can a gas strut be too strong?

Yes. An overpowered gas strut will slam the lid open dangerously, put excess stress on hinges and mounting brackets, and make it difficult to close the lid. The strut should be strong enough to hold the lid at any angle but not so strong that it overpowers the user. Aim for a safety factor of 1.2x — this gives enough reserve force without being overpowered.

How long do gas struts last?

Quality gas struts last 5-15 years depending on usage and conditions. They lose approximately 2-5% of their force per year due to gradual nitrogen leakage through the seals. Factors that reduce lifespan include: extreme temperatures, mounting rod-up (seals dry out), corrosive environments, and excessive cycling (more than 10,000 cycles). Mount rod-down for maximum life.

What is the difference between a gas strut and a gas spring?

Gas strut and gas spring are different names for the same device. 'Gas spring' is the more technically correct term used in engineering, while 'gas strut' is the common name used in automotive, furniture, and DIY applications. Both refer to a nitrogen-filled cylinder that provides a controlled pushing force. Some manufacturers also call them gas lifts or gas shocks.

Gas Strut Calculator

Application Type

Lid opens from horizontal to upright

Unit System

Lid / Door Weight

Lid Length (Hinge to Free End)

Center of Gravity from Hinge

For uniform lids, CG is at half the lid length (250 mm)

Strut Mount on Lid (from Hinge)

Strut Mount on Frame (from Hinge)

Opening Angle

Number of Struts

Safety Factor: 1.2x

1.0x (exact)1.5x (recommended)2.0x (heavy duty)

Required Force per Strut (with 1.2x safety)

660.1N

Nearest standard: 700 N gas strut

Force Summary

Required force with and without safety factor

550.1

Raw Force

660.1

Safe Force

700

Standard

Strut Dimensions

Calculated lengths based on your mounting geometry

150.0

Extended

111.8

Compressed

38.20

Stroke

Force vs. Angle

How the required strut force changes as the lid opens

Angle	Gravity Moment	Force/Strut
0°	36.77 N·m	411.2 N
10°	36.22 N·m	438.8 N
20°	34.56 N·m	464.0 N
30°	31.85 N·m	486.5 N
40°	28.17 N·m	505.9 N
50°	23.64 N·m	522.2 N
60°	18.39 N·m	534.9 N
70°	12.58 N·m	544.2 N
80°	6.39 N·m	549.8 N
90°	0.00 N·m	0.0 N

Step-by-Step Calculation

Full calculation walkthrough with your values

1
Input Values
Application: Horizontal lift
Lid weight: 15.00 kg (147.10 N)
Lid length: 500.00 mm
CG distance from hinge: 250.00 mm
Strut mount on lid: 100.00 mm
Strut mount on frame: 50.00 mm
2
Gravity Moment
Worst-case angle: 81°
Gravity moment at 81°:
M = W × d_cg × cos(81°)
M = 147.10 × 0.250 × 0.156
M = 5.75 N·m
3
Force Calculation
Perpendicular distance at 81°: 5.23 mm
Required total force: 5.75 / 5.229e-3 = 1,100.2 N
Force per strut (2): 550.11 N
With 1.2x safety: 660.14 N (148.40 lbf)
4
Strut Dimensions
Strut length closed (0°): 111.80 mm
Strut length open (90°): 150.00 mm
Extended: 150.00 mm | Compressed: 111.80 mm
Stroke: 38.20 mm

How the Gas Strut Calculator Works

Calculate the right force, length, and mounting position for gas springs

A gas strut (gas spring) supports a lid, hatch, or door against gravity by providing a controlled lifting force. This calculator determines the required force by analyzing the torque balance around the hinge point — the gas strut must generate enough moment to overcome the weight of the lid at every angle throughout its range of motion.

Gravity Moment

M = W × d_cg × cos(θ)

Weight torque about hinge

Required Strut Force

F = M / (d_perp × N_struts)

Force per gas spring

Worked Example — 15 kg Toolbox Lid

Weight

CG Distance

250

Struts

each

Force/Strut

~660

Understanding Gas Strut Specifications

Key parameters when selecting a gas spring

Gas struts are specified by three key dimensions: extended length (fully open), compressed length (fully closed), and stroke (the difference). The force rating in Newtons indicates the push force when fully extended — force increases slightly as the strut compresses due to internal gas pressure changes.

Common Gas Strut Force Ratings

50-100 N: Small cabinet doors, laptop screens

100-200 N: Toolbox lids, hatchbacks, storage boxes

200-400 N: Heavy hatches, truck canopies, industrial panels

400-800 N: Industrial machinery, large doors, bed frames

800-1500 N: Heavy equipment, agricultural machinery

Gas struts lose approximately 2-5% of their force per year due to gradual gas leakage. Choose a strut with a safety factor of at least 1.2x to account for this degradation over the strut’s lifespan.

Gas Strut Mounting Position Guide

How to choose where to mount your gas struts

Mounting position significantly affects the required force and the feel of the lid movement. Mounting the strut closer to the hinge on the lid requires higher force but produces smoother, more controlled movement. Mounting further from the hinge reduces the required force but may cause the lid to swing open quickly.

Mount Position	Force Needed	Behavior
10-15% of lid length	Very high	Slow, controlled opening; compact strut
15-25% of lid length	Moderate	Balanced feel; most common choice
25-40% of lid length	Low	Quick opening; longer strut needed
>40% of lid length	Very low	Snaps open; hard to control

Key Considerations

Important factors for gas strut selection and installation

Temperature Effects

Gas strut force varies with temperature. Force increases ~3-4% per 10°C above 20°C and decreases similarly in cold conditions. For outdoor applications, size the strut for the coldest expected temperature.

Mounting Orientation

Gas struts should be mounted with the piston rod pointing down whenever possible. This keeps the internal seals lubricated, extending the strut's lifespan from 5 to 15+ years.

Safety Factor

Always apply a safety factor of at least 1.2x. Gas struts lose 2-5% force annually from gas leakage. A 1.2x factor ensures reliable operation for 4-5 years before replacement is needed.

Center of Gravity

For uniform rectangular lids, the CG is at the geometric center (half the lid length from the hinge). For lids with uneven weight distribution, measure the balance point or shift the CG estimate toward the heavier side.

Frequently Asked Questions

Common questions and detailed answers

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Last updated Apr 22, 2026