Calculators

Calculate a laptop screen’s pixel density in pixels per inch (PPI) from its resolution and diagonal size. This uses the Pythagorean theorem and assumes square pixels. The default values are illustrative.

Calculate the viewable screen height and width from its diagonal size and aspect ratio. Results are in inches and exclude the bezel. Enter the aspect ratio from the screen specifications; defaults are illustrative.

Estimate a laptop’s current resale value using declining-balance depreciation. Enter your purchase price, age, assumed annual depreciation rate, and any additional condition-related deduction. The result is an estimate based on your assumptions, not a live market price.

Estimate the electricity cost of running a laptop using its average power draw, daily usage, billing period, and electricity rate. Use power measured at the wall when available; charger ratings are maximum outputs and may overestimate typical consumption. The estimate assumes a constant average power draw and excludes separate peripherals.

Estimate the power bank capacity needed for a chosen number of full laptop battery charges. The calculation accounts for energy lost during conversion and charging, then converts watt-hours to milliamp-hours at the power bank’s stated cell voltage. Defaults are illustrative. Actual results vary with laptop use, charging behavior, and power bank efficiency. Choose a power bank with at least the calculated capacity and check that its USB-C output voltage and wattage meet your laptop’s requirements.

Estimate charger wattage from the laptop’s required input voltage and current, with an optional headroom allowance. Check the laptop’s manufacturer specifications and choose a charger that supports the required voltage, connector, polarity, and charging protocol. Round up to an available charger wattage. Defaults are illustrative.

Estimate charging time from battery capacity, current and target charge, charger power, charging efficiency, and a taper factor. Charger power is the power available for charging after laptop use. Efficiency and taper are illustrative assumptions; charging slows near full capacity, and actual times vary. If the target is at or below the current charge, the estimate is zero.