Hobby

Estimate mowing productivity in acres per hour from your cutting width, ground speed, and efficiency — plus hours per acre and time to finish an area.

Estimate the air conditioner cooling capacity (BTU per hour) you need from your room size, using the 20 BTU per square foot rule of thumb.

Convert any wind speed in km/h to the Beaufort force (0–12) and metres per second — the scale used in marine and weather forecasts worldwide.

Find exact morning and evening blue hour times for your location. Plan your photography shoot with our calculator, featuring weather viability and phase splits.

Calculate the board feet of lumber from its thickness, width, and length using the formula (T x W x L) / 12.

Work out which ceiling fan blade span suits your room, and the airflow rating to look for when you compare models.

Work out how much concrete you need for a rectangular slab — the volume in cubic metres and the number of pre-mix bags to buy, based on each bag's yield.

Calculate how many posts and fence sections a straight fence run needs from its total length and the spacing between posts.

Work out the floor area of your room and how many boxes of laminate, vinyl, or hardwood flooring you need, including a waste allowance for cuts.

Work out how much grass seed you need to sow or overseed a lawn — the amount in kilograms and grams, based on your lawn area and seed rate.

Work out how much gravel you need to cover an area to a given depth — the volume in cubic metres and the weight in tonnes, based on the stone's density.

Estimate the heat output a heat pump needs to deliver for your home, including the allowance for hot water.

Work out how much mulch you need to cover a bed — in cubic yards, cubic feet, and standard 2-cubic-foot bags — from the area and the depth you want.

Work out how many litres of paint you need from your wall area, the number of coats, and the paint's coverage per litre.

Use our planet visibility calculator to find out which planets are visible tonight. Get exact altitude, direction, and moon glare data for your location.

Work out the flow rate your pool pump has to sustain to turn the water over in the time you want.

Estimate how many litres of rainwater you can collect from a roof from its area, the rainfall, and a runoff coefficient.

Calculate the horizontal run and sloped length of an accessibility ramp from a vertical rise and a slope ratio such as ADA 1:12.

Calculate the roof pitch angle in degrees and the slope as a percentage from a vertical rise and a horizontal run.

Find the largest standard rug that fits your room while leaving an even border of bare floor.

Find the right ski length for your height, ability, and skiing style, with a suggested range to shop within.

Calculate how many steps a staircase needs from its total rise and your target riser height, plus the exact step height once the rise is split evenly.

Enter your chest, waist and height to get the jacket number, the length letter, the EU size and the trouser waist that comes with them.

Find the recommended surfboard volume in litres for your weight, ability, and fitness — with a suggested range to shop within.

Work out how many tiles you need to cover a floor area, including a waste allowance for cuts and breakages.

Work out how many rolls of wallpaper you need to cover a wall area, including a waste allowance for pattern matching and trimming.