Measuring something accurately really depends on how much time you have. Surveying can take days, you could break out a tape measure, pace it off, guess, or, you could just Spike it using laser measuring.
Spike is a clip-on smartphone accessory that works with precision laser measuring of objects in the world around you and then augment what you capture into 3D models. Spike works by tying together smart phone capabilities, like the camera and GPS with onboard lasers, a compass, a three-axis magnetometer and Bluetooth all coordinated through a smartphone app. Spike can measure the distance to an object, object measurements, the volume and area of an object, bearing, altitude and GPS location. Once a measurement category is selected from the app, obtaining the data is as easy as using your camera; just point and shoot to capture an image up to 600 feet away and select the points to measure on the photo. All of this information can be shared from the app at any location or saved to create accurate 3-D models.
Spike is rechargeable through micro-USB and the internal battery will last for two days of typical use. Spike has several professional applications but can also be used recreationally, maybe for a small advantage on your next golf outing. Spike will be available early next year and with a fully specified API so developers can start building their own applications.
Check it out: ikeGPS