Buying LED strip lighting should be straightforward, but many customers hesitate at one key stage: calculation. How many metres do you need? What wattage will that require? Which power supply is suitable? Get these wrong and you risk dim lighting, voltage drop, overheating, or early failure.
This guide explains how to correctly calculate LED strip length and select the right driver. It will help you choose confidently from Display Lighting’s LED lighting range and match it with the correct LED power supplies and control systems.
Step 1: Measure the Total Length Required
Start with a precise measurement of the area where the strip will be installed.
For example:
- Under-cabinet kitchen run: 3.6 metres
- Retail shelving: 8.4 metres across multiple bays
- Cove lighting: 12 metres around a perimeter
Always measure the actual surface where the strip will sit, not just the wall length. Account for corners, returns and vertical sections.
Round up slightly to allow for cutting increments. Most LED strip lighting can only be cut at specific marked points.
Step 2: Identify the Wattage per Metre
Every LED strip has a power rating expressed in watts per metre. For example:
- 5W per metre for low-output accent lighting
- 10W per metre for general lighting
- 15W per metre or higher for task or display lighting
This specification is listed within the product details in our LED strip lights.
Step 3: Calculate Total Wattage
Use this simple formula:
Total length in metres × watts per metre = total wattage required
Example 1: Residential kitchen
- Length: 4 metres
- Strip rating: 10W per metre
- 4 × 10 = 40watts total load
Example 2: Retail shelving
- Length: 10 metres
- Strip rating: 115W per metre
- 10 × 14.4 = 150 watts total load
This figure tells you the minimum output your power supply must support.
Step 4: Add Headroom to Protect the System
Power supplies should never run at 100 percent capacity. Running a driver at full load increases heat and shortens lifespan.
Industry best practice is to allow at least 10% headroom.
Using the kitchen example:
- 38.4W required
- Add 10 percent
- 38.4 × 1.1 = 42.24W
You would select a 60W power supply to allow safe operating margin.
For the retail example:
- 144W required
- 144 × 1.1 = 158.4W
- You may use a 200W driver or split the load across multiple drivers
Browse our full range of compatible LED power supplies and control systems to match your calculated load correctly.
Step 5: Consider Voltage Drop
Voltage drop is one of the most common issues in long strip installations. It causes dimming towards the end of the run and inconsistent colour temperature.
The longer the run, the more voltage drop becomes a factor.
General guidance:
- 12V strips are best kept under 5 metres per feed
- 24V strips can often run up to 10 metres per feed
If your project exceeds these lengths, you have two options:
- Power injection
- Split the run into multiple sections
When to Inject Power
Power injection means feeding power into the strip at additional points rather than from just one end.
You should consider power injection when:
- Runs exceed recommended lengths
- You notice brightness fading at the far end
- High-output strips are used
- Commercial lighting requires uniform brightness
In a retail example with 12 metres of 24V strip, you might power the strip from both ends or inject power midway to maintain consistent illumination.
Our team can assist with layout planning to ensure your LED strip lighting performs evenly across long installations.
The Role of Aluminium Profiles
Heat management is essential for both performance and longevity. Installing LED strips directly onto timber or plasterboard can trap heat.
Using aluminium LED profiles helps:
- Dissipate heat effectively
- Maintain brightness stability
- Protect the strip from dust and damage
- Create a clean architectural finish
For kitchens, offices, and retail shelving, aluminium channels are strongly recommended.
Practical Residential Example
Project: Under-cabinet kitchen lighting
- Length: 5 metres
- Strip rating: 9.6W per metre
- Total load: 48W
- Add 10 percent headroom: 58W
Recommended solution:
- 24V LED strip lighting
- 75W driver from our LED power supplies and control systems
- Installed in slimline aluminium profiles
This setup provides safe operation, long lifespan and even brightness.
Practical Commercial Example
Project: Retail shelving display
- Length: 12 metres
- Strip rating: 14.4W per metre
- Total load: 172.8W
- Add headroom: 207W
Recommended solution:
- 24V high-output LED strip lighting
- Two 150W drivers or one 240W driver split across zones
- Power injected at both ends
- Mounted within aluminium profiles
For projects requiring rigid performance or very long straight runs, you may also consider LED light bars as an alternative for improved structural stability and simplified installation.
Buy LED Strip Lighting with Confidence
Display Lighting supplies high quality LED strip lighting, reliable LED power supplies and control systems, and durable aluminium LED profiles designed for residential and commercial environments.
If you are unsure about wattage, voltage or layout, our team can assist with product selection to ensure your lighting performs exactly as intended.
