LED driver sizing calculator
On constant-voltage strip jobs the usual failure is not a dead driver but voltage drop — the far end of the run is visibly dimmer. This calculator works back from a 5% drop limit to the cable size and adds driver headroom.
- Working current
- —
- Recommended driver wattage
- —
- Allowed voltage drop
- —
- Copper cross-section
- —
Formulas and assumptions
- Working current I = P ÷ V (P total load, V output voltage)
- Recommended driver wattage = P × 1.2 — 20% headroom so the driver is not run at full load continuously
- Allowed drop ΔV = V × allowed %; maximum loop resistance Rmax = ΔV ÷ I
- Copper cross-section S = ρ × 2L ÷ Rmax (ρ = 0.0175 Ω·mm²/m, 2L for the return path)
I = P / V
P_driver = P × 1.2
ΔV = V × drop%
R_max = ΔV / I
S = ρ × 2L / R_max (ρ = 0.0175 Ω·mm²/m)
Beyond about 5% drop the dimming at the far end is visible to the eye. If the answer is already over 4 mm², it is cheaper to raise the output voltage (12V → 24V) or split the run into shorter feeds than to keep making the cable thicker.
Need a model number? Send us the wattage, voltage, run length and dimming method — we will match it against 47 in-stock models.
Contact →