Every home and garden project starts with a number. The paint, tile, flooring and wallpaper calculators tell you how much to buy before you head to the store. Square footage, concrete, gravel, mulch and fence calculators work out the material for outside jobs, and the BTU calculator sizes an air conditioner or heater for a room. The electricity cost calculator shows what an appliance costs per month at your rate, the grow light cost calculator adds up the power bill for a whole grow, and the VPD calculator shows whether your grow room air suits your plants.