Counting fixtures
The fixture-count mode takes a run length and a target spacing and finds a whole number of fixtures that spaces them evenly. On an open run, such as a path, there is a light at each end, so the count is the number of gaps plus one. On a closed loop, such as a light around a circular bed, the last gap returns to the first fixture, so the count equals the number of gaps. In both cases the calculator shows the actual spacing, which may differ slightly from your target so that there is no odd leftover gap. The spacing presets of 4, 6, and 10 feet are starting points for path, border, and accent lighting; the right spacing depends on each fixture’s light spread, so check the manufacturer’s guidance.
Why voltage drop matters
Low-voltage landscape lights run on a transformer, and every foot of wire has some resistance. As current flows, part of the voltage is lost in the wire, so fixtures far from the transformer receive less than the system voltage and can look dimmer. The voltage-drop mode estimates this loss. It divides total wattage by system voltage to get current, multiplies the wire resistance for your gauge by twice the one-way distance (current travels out and back), and multiplies the two to get volts dropped.
The calculator uses typical resistance values for solid copper wire per 1,000 feet: 4.016 ohms for 16 AWG, 2.525 for 14 AWG, 1.588 for 12 AWG, and 0.999 for 10 AWG. A smaller AWG number means thicker wire and less drop. The result is flagged as healthy at 3% or less, borderline up to 10%, and too high above that. It treats all the wattage as if it were at the far end of the run, which is a conservative simplification.
Fixing a high drop
If the drop is too high, the usual options are a thicker wire gauge, a shorter run, less wattage on the run, or splitting the fixtures into two runs from the transformer. Some transformers also offer higher voltage taps for long runs; follow the transformer and fixture instructions. This tool gives planning estimates only, not electrical advice, so follow the product instructions and local codes, and use a qualified electrician for line-voltage work.
How to use the landscape lighting calculator
- Measure the run length in feet along the path or bed edge.
- Enter a target spacing or choose a preset, and pick open run or closed loop.
- Note the fixture count and the actual even spacing.
- Switch to Voltage drop and choose the system voltage of your transformer.
- Add up the wattage of all fixtures on the run and enter it with the one-way distance from the transformer.
- Choose the wire gauge and read the result; if it is borderline or too high, try a thicker gauge or split the run.
