GardenCalcs.uk
Garden Lighting Calculator — Lights, Cable & Cost
Calculate how many garden lights you need, cable lengths, transformer size, and total costs.
Total run to be lit — path lights are placed every 1.5-3m
Uplighters for trees, walls and focal points (~5W each)
Recessed step and deck markers (~1W each)
Mains 12V is brighter and reliable; solar needs no wiring
Default: 2m apart
Default: 3W LED
Default: £15 per light
Default: 28p/kWh
Default: 5 hours per night
How We Calculate This
How The Calculations Work
- Path lights: (path length / spacing) + 1
- Cable length: Sum of path runs + feature runs (~5m each) + deck runs (~1.5m each) + 5m for main run
- Transformer: Total wattage x 1.2 safety margin, rounded up to nearest 10W
- Running cost: (Total watts / 1000) × hours × 365 × electricity rate
Material prices are indicative UK retail estimates: 12V low-voltage transformers run roughly £25-£90 across the 60-300W bands, and 1.5mm² two-core outdoor cable about £1-£2 per metre. Always confirm against current supplier prices for your chosen brand.
Frequently Asked Questions
Path lights should be spaced 1.5-3 metres apart depending on their brightness and spread. Closer spacing (1.5-2m) gives more even light; wider spacing (2.5-3m) creates pools of light for a more dramatic effect. Stagger lights on alternate sides for the best look.
Add up the total wattage of all lights and choose a transformer rated at least 20% higher. For example, 10 lights at 3W each = 30W, so use a 40W or 60W transformer. This headroom allows for cable voltage drop and future additions.
Mains LED lights are brighter, more reliable, and last longer. Solar lights require no wiring but are dimmer, weather-dependent, and batteries need replacing every 1-2 years. Mains is best for paths and security; solar works for decorative accent lighting.
LED garden lights are very cheap to run. The exact cost depends on the number of fittings, their wattage and your tariff: a typical 15-20 light scheme totalling 30-50W and running 5 hours a night costs roughly £5-£20 a year at a 28p/kWh electricity rate (for example, 39W × 5 hours × 365 nights × £0.28 = about £20). Lower-wattage decorative fittings sit at the bottom of that range. Solar lights cost nothing to run but have higher upfront costs and shorter lifespans.
Most low-voltage garden lights use 12V systems with 1.5mm² two-core outdoor cable. Runs over 20 metres may need 2.5mm² cable to reduce voltage drop. Always use cable rated for direct burial or run it through conduit.
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Last updated: March 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.