Pinhole Camera Information I found

Camera Length	Needle Size	Diameter of hole	Relative f/stop
8″	8	.023″	f/350
6.5″	9	.020″	f/300
5″	10	.018″	f/280
4″	12	.016	f/250
2.5″	13	.013	f/190

or you could use this formula…
dia/focal length

or…

the optimum pinhole = the sq.root of 0.0016
multiplied by the pinhole to film distance…

(or you can wing it…)

Making exposures?…Start here

Weather Conditions	f/stop	Photo paper	ASA 125	ASA 400
Bright or hazy sun. A scene with light sand or on snow.	250 300 350	17 seconds 29 seconds 44 seconds	1 second 1.6 seconds 2.5 seconds	1/4 second 1/3 seconds 1/2 second
Bright or bright-hazy sun. The shadows are distinct (sharp) Your typical nice, sunny type day.	250 300 350	49 seconds 1.3 minutes 2.1 minutes	2.8 second 4.6 seconds 7.1 seconds	1 second 1.25 seconds 1.5 seconds
Weak or hazy sun. The shadows aren’t distinct (soft) An OK type day.	250 300 350	2 minutes 3.3 minutes 5.1 minutes	6.7 seconds 11 seconds 17 seconds	1.3 seconds 2.2 seconds 3.4 seconds
Cloudy. But bright! No shadows No sun. No rain.	250 300 350	5.4 minutes 9 minutes 14 minutes	18 seconds 31 seconds 47 seconds	3.6 seconds 6 seconds 9.2 seconds
Open Shade or heavily overcast No shadows Either a grey day or in the shadow of a tall building	250 300 350	14 minutes 23 minutes 36 minutes	47 seconds 1.3 minutes 2.0 minutes	9.2 seconds 15 seconds 24 seconds
Dawn or Dusk Dark out here… Like it says. Early morning or early evening	250 300 350	38 minutes 1 hour 1.6 hours	2.1 minutes 3.5 minutes 5.4 minutes	25 seconds 42 seconds 1 minute

Ok. Keep in mind that all these times are just starting points. As you make more exposures and get better at making guesses that work you’ll make your own exposure chart.

When you make an exposure that is just way too dark as a print then double the exposure you gave the neg. If your print is just too light then halve the exposure. It might sound like the long way around but by splitting the differences each time you can arrive at a pretty good exposure in a your first few attempts.

Another great idea is to keep a notebook of all your exposures, the weather conditions, the film or paper etc.

*All of this information I got off of this website ... http://www.pinhole.org/exposure-guides/