Look at some of the seed companies and what they put in a pack. 20 carrot seeds may be a meal or two, but 20 squash seeds will yield a LOT of squash! Think in terms of harvest. For what it's worth, I have pretty much given up on trading here (except for special varieties) because I'm tired of trading 10 tomato seeds for 10 lettuce seeds. Obviously, the tomato way outproduces the lettuce! postage is high, and it has started costing more to trade a few seeds here than to get "too many" commercial seeds. If people would include more seeds, I could afford it. That's my rant.
When I was trading, I always counted out the seeds for each order as it came in. That way I could offer each person how many they wanted.

10-25 depending on size of large seed to small or how much came in that year in the garden If I have a nice trade I give more back too.
Sometimes i feel some people dont give much I understand some are from trades or not to many on hand but if you have them share them. Big squash seed smaller trades and letting who you are trading with know is important.

An easy way is to have 25 be the standard, but measure for ease. I eyeball it, and for tiny seed 1/8 t is good, radish 1/4 or slightly less, for medium seeds like hollyhocks or similar 1/2t - 1t. for larger, like beans, just count them. I generally am sending much more seed than I promise, but it is easier/faster.

I would use 137 radish seeds easily - remember 13-26 will not sprout, 13-26 will be eaten by the birds. Of the remaining 85 -111, 13-26 will be destroyed buy bugs or disease, leaving about 59-98 for me to eat.

10-20% no grow
10-20% birds
10-20% bugs or other critters
the rest for me.

My FIL says something like plant 1 for the critters, 1 for the bugs, and 1 for yourself. That takes 137 seeds down to about 45 radishes. Now, I sure don't want that many tomatoes, but radishes, carrots, other small seeds, yes.

If you are wanting to maximize your seed trades compared to your seed stock, read the FAQ for this seed eschange forum, stick with the standard numbers (which is pre-figured out for general traders preferences), and count seeds.

I totally agree with kilngod.

I aim for 24-30 seeds when they are "countable" (but not bigger than beans or corn.) I have TONS of some of my seeds, and really enjoy sharing them, so I send more. Some of the seeds I receive are so tiny, they are like dust. I go with the rule of thumb that if seeds are uncountable, 1/8 teaspoon is plenty.

Unlike Jedonne's opinion, many of the seeds I seek are natives and can be hard to come by, so I really appreciate the opportunity to trade seeds with folks who have seeds that are not commonly available. And trading seeds on GW allows you to test a small sample of something you may never have tried otherwise. I have found some real gems in the heirloom veggies this way (Thank you, GW Members!).

In my opinion, being open and honest, and listing what you typically send in a seed pack on your exchange page is important. Additionally, those huge seeds like pawpaw trees, acorns, and buckeyes ... 6 seeds fills a lot of room and should be plenty!

I package my own seeds and try to mimick what commercial seed packs have.

I actually count the "uncountable" and weigh them with a small scale, so I know the weight of approximately 100 or 200 of the small or 25-50 of medium. Large ones you can count easily enough. I don't expect everyone to do this, but I think it makes the expectations clear enough. I am also not extremely worried about cleaning every bit of dust from the seeds. I just weigh out more and make sure they aren't cheated.

Then I just label how many seeds (or approximately). I also write the date of seed harvest on the packet and I place a piece of activated carbon in the small plastic ziploc to make sure that the moisture is absorbed (it is a piece from a bottle of fish tank filter medium). For example, my packs of Columbine seeds are labeled as "over 500" and they come out to about 1 gram of seed.

I think that people expect a reasonable amount of viable seed. If someone is trading seed that is older,I would expect them to include more. Basically, I treat others the way I would want to be treated.

1. Communicate, communicate, communicate. Talk about what you expect and what you want. Tell others what you are sending them.
2. Label. (Also communication.) List name of seed, year harvested, # of seeds or weight. The more information you can provide the more informed you look. You don't look like some fly-by-night ding dong that throws seeds in a baggie and floats them through the mail.
3. Send with protection. Use bubble wrap or bubble envelopes. There are FAQs on this so read it there. Don't send green bean seeds unprotected through USPS. All the person will receive is green bean dust when it goes through the sort machine. You've saved 35 cents, but you've made an enemy.
4. Use Rate and Review. It works well for Ebay and works well here, too. Find the person on Rate and Review and see what people are saying. If the posts are negative, politely decline any trades.
5. Package well. If you use plastic baggies make sure they are labeled and the seeds are dry. I have received moldy seeds. If you use things like recycled tea bags make sure the person can read it clearly when you label it. I've had too many seeds I couldn't read the label. Be careful what shortcuts you use. WBHV stumped me for w years. White bleeding heart vine. Write it out.
6. I thougth people were crazy for keeping a list of trades. It's the smartest thing I ever did. Now I can look back and see if I traded with them before, how the trade went, and what we traded. I thought I could remember...and maybe you can...but I can't. It takes a little time, but saves me frustration, postage and a lot of heartache.
7. Most of us think of our seeds as our babies. It's like finding a home for kittens. We want each home to appreciate and care for our seeds. We want the person to be happy. There's always a few 'ringers' in every circle and there are some here, too. Most are very generous, loving and caring. They want you to be happy and they want to be happy.
Heidi in Nebraska
Oh, and I created paper envelopes for seed saving. They are on pinterest. They are free. Just print as many as you want. I like paper because it allows the seeds to dry and not mold.
Look up Seed Envelopes. There are about 8 envelopes per page.