Getting the most out of your home lighting means understanding the numbers behind it. This collection includes the LED Savings Calculator to show how much switching from incandescent or CFL bulbs saves over time, the Recessed Lighting Spacing Calculator for laying out even coverage, the Lumens to Watts Calculator for choosing the right replacement bulb, and the Daily Light Integral Calculator for plant-growth lighting design.
Browse the Popular list to find the tools smart-home planners and DIY electricians rely on most, or open the Trending tab for newly added calculators. Every tool is free, needs no login, and works on any device — handy whether you are standing in the lighting aisle or mapping out a grow room.
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Running Amps and Startup Load CalculatorSize a generator by adding running watts plus the largest startup surge. Enter your appliances to find the minimum wattage and a recommended size.
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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.
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mAh to Wh Battery Capacity CalculatorConvert battery capacity from mAh to Wh instantly. Enter milliamp-hours and voltage to get watt-hours and kilowatt-hours for any battery.
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CADR & Room Size CalculatorFind the maximum room size an air purifier can handle from its CADR rating. Calculate floor area in sq ft for any target air changes per hour (ACH).
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IP Subnet & Host Count CalculatorCalculate usable hosts, subnet mask, wildcard mask and total addresses from any IPv4 CIDR prefix (/0 to /32). Free subnetting tool.
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Lux to Lumens CalculatorConvert lux to lumens instantly. Multiply illuminance (lux) by the illuminated area in square metres to get total luminous flux in lumens.
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IoT Sensor Battery Life CalculatorEstimate how long an IoT sensor or wireless device will run from its battery using capacity (mAh), average current draw (mA), and a usable-capacity derating factor.
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Room Lighting Lumens CalculatorCalculate how many lumens a room needs based on its size and lighting purpose. Enter length, width, and light level to get total lumens and bulb count.
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Lumens to Lux CalculatorConvert lumens to lux instantly. Enter luminous flux (lm) and the illuminated area in m² to find illuminance (lux = lumens ÷ area).
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Watts to Lumens CalculatorConvert watts to lumens instantly. Enter power in watts and luminous efficacy (lm/W) to find the light output in lumens for LED, CFL or incandescent bulbs.
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Light Bulb Energy Cost CalculatorCalculate the yearly, monthly and daily electricity cost of running a light bulb from its wattage, hours used per day and your price per kWh.
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Coefficient of Utilization (Lumen Method) CalculatorCalculate how many light fixtures you need using the lumen method with coefficient of utilization (CU) and light loss factor (LLF).
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PPFD to DLI CalculatorConvert PPFD (µmol/m²/s) to DLI (mol/m²/day) using your grow light's intensity and daily photoperiod. Free, instant grow-light calculator.
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Lumens to Candela CalculatorConvert lumens to candela using the beam apex angle. Free lumens-to-candela calculator with solid angle output, formula, and a worked example.
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Inverse Square Law Light Intensity CalculatorCalculate light intensity at a new distance using the inverse square law E₂ = E₁ × (d₁/d₂)². Free physics & lighting tool for lux and illuminance.
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Candela to Lumens CalculatorConvert candela (cd) to lumens (lm) using luminous intensity and beam apex angle. Free, accurate candela-to-lumens converter with solid angle output.
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Luminous Efficacy CalculatorCalculate luminous efficacy in lumens per watt (lm/W) from a light source's luminous flux and electrical power. Fast, free, and accurate.
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Lumens per Square Foot CalculatorCalculate foot-candles (lumens per square foot) from total lumens and room area. Free lighting calculator with instant lux conversion.
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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.
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HVAC BTU Calculator — AC Size by RoomCalculate the BTU cooling capacity you need by room size. Enter length, width, occupants and sun exposure to size your AC unit correctly.
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kWh to Cost CalculatorCalculate the cost of electricity from kWh used and price per kWh, or from device watts and hours of use. Fast, accurate energy cost estimates.
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LED Series Resistor CalculatorCalculate the correct series resistor for an LED from supply voltage, LED forward voltage, and current. Get resistance and power rating instantly.
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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.
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Watts to Lumens CalculatorConvert watts to lumens using luminous efficacy (lm/W). Compare LED, CFL and incandescent brightness instantly with this free calculator.
Frequently asked questions
What can I calculate in the Smart Home and IoT section?
The collection focuses on lighting: illuminance unit conversions (lux and foot-candles), lumens-to-watts equivalences, recessed-light spacing and room layout, LED running cost and long-term savings versus incandescent and CFL over a 15-year horizon, watts-to-lux conversion, and daily light integral (DLI) for horticultural lighting. Together they cover both home improvement and grow-room design.
How accurate are the lighting and energy savings calculations?
Tools apply standard photometric formulas and use the electricity rates you supply to project costs. Long-term savings figures are indicative estimates — actual results depend on usage patterns and local tariffs. For safety- or code-critical electrical installations, verify against the relevant electrical code (such as the NEC in the U.S.) and have a qualified electrician or engineer review the design.
Do I need to pay or create an account?
No. Every calculator is completely free and open without registration. Load the page, enter your values, and get your result instantly — no sign-up, no fees, no limits on usage.
Are my energy usage data or home details stored?
No. All calculations run locally in your browser. Nothing you enter — wattage, room dimensions, electricity rates — is sent to or retained by our servers. Your home data stays entirely on your device.
How do I find the most popular smart home calculators?
The default category view orders tools by real visitor usage, so the most-relied-upon calculators appear first. The Trending tab shows which tools are seeing a recent uptick in interest — useful when planning a lighting upgrade, retrofit project, or new grow setup.
