SANDBAGS: How heavy and how many?

I need to pick up some sand bags for my light stands. It seems even on calm days I'm always having to worry about the wind catching my umbrellas and toppling things over.

Is one "saddle-style" sand bag per light stand enough? How heavy do they need to be? Weight is not really an issue since I have a large wheeling trap case to move my lighting stuff around in.

Shopping for sand bags feels like I'm shopping for orange juice, there's so many varieties!

I will usually place 2 bags per stand unless it is windy or needs more. These are roughly 15 pounds each. I have 4 of the cowboy studio bags these are well built and reasonably priced. $11 for 2 through Amazon.
The only thing I do not like is they are little long when hung over the legs. My set that I made are shorter and actually hold better.

Same here, 2 bags a stand, 5kg per bag (11pounds).

Better put one to many then one to little!

Remember some of the cheaper bags rip or leak so it will probably be a good idea to put the sand in ziploc bags or even use gravel, or even lead balls to make them weigh more

Also since my main job is working at an orange juice plant I would always buy Tropicana, they have the cleanest plants I have worked at,and the highest quality standards. Now that the clear bottles have been introduced take a look at the difference in the pulp in the bottles, the high quality fresh pulp is more dense so it sinks to the bottom. If you notice simply orange also has pulp floating its because they also use frozen 2nd quality pulp.
Also take a notice at how many black specs are in the pulp at the bottom of the container, that is from oranges that freeze while on the tree, which is called black heart, where the tree kills the fruit off to survive the rest of the winter and the fruit rots.

To calculate for a certain wind speed and its effect on a 'sail' of a given area...

Force, F = A x P x Cd

where

A = The projected area of the item,
P , Wind pressure (psf), = .00256 x V^2 (V= wind speed in Mph)
Cd , Drag coefficient, = 2.0 for flat plates.

So if you use a 36" umbrella, it has a projected area of about 7 sq.ft.
If wind speed is 10 mph, the wind pressure is 0.256 psf
So pressure is 3.6 lbs, assuming the drag coefficient of a flat plate

Of course, then you need to factor in the multiplicative effect of the placement of the 'sail' at the end of a lever arm (the light stand)

Wilt, I'm going to nominate you for the "Measurebater of the Month" award!

+1 on the recommendation for gravel. I picked that tip up from David at strobist.com on his latest DVD set. It's cheap and way less messy. Just go to Lowes or Home Depot and get pea gravel. One bag will fill a few sandbags.

Being in the Physical Therapy supply business for over thirty five years did have it's advantages. One being the access to Cuff Weights. These durable assorted weights are wrapped around the ankle to add additional weight for leg extensions during rehabilitation. Since that market has dried up, the cuff weights are used in my studio for all of my light stands. Another item is a rolling cart and stool for well being of the photographer.
If interested, let me know.

Ankle weights work pretty much the same. I used a set for a while simply because I saw them at walmart on clearance and got them cheap.

PhotosGuy wrote in post #13642740
Wilt, I'm going to nominate you for the "Measurebater of the Month" award!

Sorry, but I certainly do not qualify for that distinction...I tested nothing, I measured nothing, I reported nothing for this thread. I merely offered a way to calculate how many sandbags to use on any given day, which is what the topic of the thread requested!

Wilt wrote in post #13645052
Sorry, but I certainly do not qualify for that distinction...I tested nothing, I measured nothing, I reported nothing for this thread. I merely offered a way to calculate how many sandbags to use on any given day, which is what the topic of the thread requested!

I'd ask you what time it is but I don't want to know how to build a watch...

FlyingPhotog wrote in post #13645080
I'd ask you what time it is but I don't want to know how to build a watch...

I would not provide that information, because that was not the OP subject title!
How to estimate how many sandbags and how much weight was asked...I provided some pertinent information.

Wilt wrote in post #13640728
To calculate for a certain wind speed and its effect on a 'sail' of a given area...

Force, F = A x P x Cd

You could add a factor cos(azimuth) cos(tilt)

Wilt wrote in post #13640728
To calculate for a certain wind speed and its effect on a 'sail' of a given area...

Force, F = A x P x Cd

where

A = The projected area of the item,
P , Wind pressure (psf), = .00256 x V^2 (V= wind speed in Mph)
Cd , Drag coefficient, = 2.0 for flat plates.

So if you use a 36" umbrella, it has a projected area of about 7 sq.ft.
If wind speed is 10 mph, the wind pressure is 0.256 psf
So pressure is 3.6 lbs, assuming the drag coefficient of a flat plate

Of course, then you need to factor in the multiplicative effect of the placement of the 'sail' at the end of a lever arm (the light stand)

Wilt - could you do this again and factor in a bird flying by?

Wilt wrote in post #13640728
To calculate for a certain wind speed and its effect on a 'sail' of a given area...

Force, F = A x P x Cd

where

A = The projected area of the item,
P , Wind pressure (psf), = .00256 x V^2 (V= wind speed in Mph)
Cd , Drag coefficient, = 2.0 for flat plates.

So if you use a 36" umbrella, it has a projected area of about 7 sq.ft.
If wind speed is 10 mph, the wind pressure is 0.256 psf
So pressure is 3.6 lbs, assuming the drag coefficient of a flat plate

Of course, then you need to factor in the multiplicative effect of the placement of the 'sail' at the end of a lever arm (the light stand)

Wilt, you always have the math covered...