Plan landscape circuits with clear wire recommendations today. Avoid dim fixtures by limiting voltage loss. Compare gauges, costs, and lengths before you buy anything.
Current is estimated from load and voltage: I = P / V. Voltage drop is estimated using round‑trip length: Vd = 2 × L × I × R.
L is one‑way length (feet), R is resistance per foot from the gauge table. The recommended gauge is the smallest that meets both voltage drop and adjusted ampacity.
| Voltage | Load (W) | Length | Max Drop | Material | Typical Pick |
|---|---|---|---|---|---|
| 12 V | 60 | 50 ft | 3% | Copper | 12–14 AWG |
| 12 V | 120 | 100 ft | 5% | Copper | 10–12 AWG |
| 24 V | 120 | 100 ft | 3% | Copper | 12–14 AWG |
These examples are illustrative. Always verify with your product specs and local requirements.
Landscape lighting often fails from excessive voltage loss, not fixture defects. This calculator estimates current from watts and supply voltage, then applies round‑trip resistance to predict drop at the end of the run. Use it during layout to decide whether one long feed is acceptable or whether branching, looping, or home‑run wiring is better for uniform brightness. It also highlights how distance multiplies losses as loads increase.
Selecting a thicker conductor lowers resistance per foot, which reduces drop and improves efficiency. The tool tests multiple gauges and selects the smallest size that meets your chosen drop limit. For low‑voltage systems, small percentage changes matter because the supply voltage is already low. A 1‑volt loss on 12V can visibly dim LEDs. Larger gauges can also reduce transformer strain at start‑up.
Wire must also carry current safely. The calculator compares estimated load current, plus a user‑set safety margin, to an adjusted ampacity. Ambient temperature and bundled conductor count apply simple derating factors to reflect reduced heat dissipation. These checks help prevent warm cable, insulation stress, and performance drift in continuous evening operation. Keep connections tight to avoid localized heating at splices.
Garden lighting evolves with seasons and new beds. Adding a margin allows extra fixtures without rewiring and helps cover real‑world losses from connectors, splices, and transformer tolerances. When results show no gauge meets your limits, treat it as a design signal: shorten runs, split circuits, increase system voltage, or move the power source closer. Consider multiple taps so each zone stays within a target drop.
After submitting, export results to CSV or PDF to document assumptions for installers or future maintenance. Record the chosen voltage, total wattage, one‑way length, and allowed drop so upgrades stay consistent. Always confirm final selections against your cable’s insulation rating, burial method, and local requirements, and test brightness at the farthest fixture before backfilling. A quick meter check validates drop under real load conditions during peak evening hours.
For most garden lighting, aim for 3% to 5%. Tighter targets improve uniform brightness, but may require thicker wire or shorter runs. LEDs can tolerate some drop, yet visible dimming often starts around one volt on 12V systems.
Current travels to the fixture and returns on the other conductor, so the circuit includes both directions. The calculator uses one‑way distance and doubles it to estimate total resistance in the loop for voltage drop.
Enter the total watts of the fixtures on that specific run. Transformer rating is only a supply limit. If you have multiple branches, calculate each branch separately and size wiring for the branch current.
Higher ambient temperatures reduce how much current a wire can carry continuously. The calculator applies a simple derating factor so the recommended gauge keeps additional headroom when cables run through hot soil, enclosures, or tightly packed conduits.
It can be used in some installations, but it has higher resistance and needs larger sizes for the same drop. Connections also require compatible hardware and proper torque. Many landscape kits assume copper conductors, so confirm with your product specifications.
Treat it as a design change request. Reduce the run length, split the load into zones, move the power source closer, increase system voltage, or allow a higher drop limit. Recalculate after each change to confirm performance.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.