The Recessed Lighting Calculator and Recessed Lighting Spacing Calculator eliminate fixture layout guesswork, the Lumens to Watts and Watts to Lux calculators let you compare bulbs on equal footing, and the 15-Year Incandescent vs CFL vs LED Running Cost Comparison shows exactly what switching saves. Growers can also use the Daily Light Integral Calculator to hit precise plant lighting targets.
Browse the full list — ordered by how often other users open each tool — or open the Trending tab for what's popular right now. Every calculator is free, requires no account, and works on any device.
-
Lumens Needed CalculatorCalculate how many lumens you need to light a room. Multiply floor area (m²) by the recommended lux level to get total lumens for any space.
-
LED Wire Voltage Drop CalculatorCalculate the voltage drop in wires feeding an LED or LED strip. Enter current, length, wire area and material to find loss, voltage at the LED and power waste.
-
Christmas String Light Count CalculatorFind how many Christmas string lights you need to cover a given length and the total wattage they draw. Quick holiday lighting planner.
-
LED Payback Period CalculatorCalculate how fast an LED bulb pays for itself. Enter wattages, usage hours and electricity rate to see annual savings and payback in years.
-
LED Bulb Lifespan CalculatorConvert an LED bulb's rated lifespan in hours into years based on daily usage. Find out how long your LED bulbs will really last.
-
Average Illuminance CalculatorCalculate average illuminance (lux) from light fixtures using the lumen method: fixtures, lumens, coefficient of utilization, light loss factor and area.
-
Projector Brightness (Nits / Foot-Lamberts) CalculatorCalculate projector screen brightness in foot-lamberts (fL) and nits from lumens, screen gain, and screen size. Free, instant home-theater tool.
-
Lux to PPFD Conversion CalculatorConvert lux to PPFD (µmol/m²/s) using source-specific conversion factors for sunlight, LED, HPS and more. Free grow-light photosynthetic light estimator.
-
TV/Projector Viewing Distance CalculatorFind the ideal TV or projector viewing distance from screen diagonal, aspect ratio, and preferred viewing angle (SMPTE 30°, THX 40°).
-
LED Current Limiting Resistor CalculatorCalculate the series resistor needed to safely drive an LED. Enter supply voltage, LED forward voltage, and current to get resistance and power rating.
-
Projector Screen Size CalculatorConvert a diagonal screen size and aspect ratio into exact width, height and area in inches and centimeters for projectors and TVs.
-
Lighting Watts to Amps CalculatorConvert lighting watts to amps instantly. Enter total fixture wattage, voltage, and power factor to find the current draw for sizing circuits and breakers.
-
Lighting kWh Usage CalculatorCalculate the kWh energy used by your lighting and its cost. Enter bulbs, watts, hours per day and days to estimate consumption and electricity bills.
-
Maximum Lights per Circuit CalculatorFind how many light fixtures you can safely put on a circuit. Enter voltage, breaker amps and watts per fixture to get the max count at the 80% rule.
-
Number of Bulbs Needed for a Room CalculatorFind how many light bulbs you need for a room. Enter room area, desired light level, and lumens per bulb to get the count.
-
Foot-Candles to Lux CalculatorConvert foot-candles (fc) to lux (lx) instantly. Enter an illuminance value and get the exact result using lux = fc × 10.7639.
-
Lux to Foot-Candles CalculatorConvert lux to foot-candles instantly. Enter an illuminance value in lux and get the equivalent foot-candles using fc = lux / 10.7639.
-
Lumens Needed CalculatorCalculate how many lumens you need to light a room. Enter room size and type to get the total lumens required for proper, comfortable brightness.
-
Grow Light Coverage Area CalculatorCalculate how many square feet your grow light covers from its PPF output and your target PPFD. Free, instant grow tent coverage area calculator.
-
LED Equivalent Wattage CalculatorConvert incandescent bulb wattage to its equivalent LED wattage. Estimate lumens, LED power draw, and energy savings using bulb efficacy.
-
Candela to Lux CalculatorConvert candela (cd) to lux (lx) using luminous intensity and distance. Free candela-to-lux calculator with the formula lux = cd / distance².
-
LED Series-Parallel Array CalculatorCalculate the series resistor, voltage drops, current and power for an LED array with multiple parallel strings of LEDs in series.
-
Watts to Lumens CalculatorConvert watts to lumens using luminous efficacy (lm/W). Compare LED, CFL and incandescent brightness instantly with this free calculator.
-
LED vs Incandescent Bulb Savings CalculatorCalculate how much money and electricity you save each year by switching from incandescent bulbs to LEDs based on wattage, usage hours and energy price.
Frequently asked questions
What lighting problems can I solve with these calculators?
The collection covers room and fixture layout (spacing, quantity, and lumen output for recessed lighting), bulb comparison and energy savings, unit conversions between lumens, watts, lux, and foot-candles, LED upgrade cost analysis, and horticultural lighting planning via the Daily Light Integral Calculator.
How accurate are the spacing and energy savings results?
The calculators use standard illumination formulas and published bulb wattage data. Results are solid planning estimates. For safety- or code-critical lighting installations, verify your design against the relevant electrical and building codes and have a qualified electrician or lighting designer review the final plan before proceeding.
Is any data I enter stored or shared?
No. All calculations run entirely in your browser. Room dimensions, fixture counts, and energy cost figures you enter are never sent to or saved by our servers.
Which lighting calculators do people use most?
The Lumens to Watts Calculator and LED Savings Calculator are consistently the most visited, followed closely by the Recessed Lighting Calculator. The list is ranked by real-world usage, and the Trending tab highlights which tools are gaining traffic right now.
Are these tools free to use?
Completely free — no account, no subscription, no hidden charges. Open any calculator on your phone, tablet, or laptop and get your answer in seconds.
