This is a question only you can answer. How many germinated seedlings do you need for your experiments (including appropriate number of replicates plus some spares)? What are the required germination conditions - temperature, moisture, spacing, media, exposure to light, dormancy? How much seedling development is required - maybe seedlings need to be transplanted to pots or to the field after a certain period? If the seeds are fresh, and been stored appropriately, the viability should be high and the vast majority should germinate.

It depends upon you, what experiment you want to do. Plant seeds according to your need in your experiment, and also provide required space for each plant.

There is no formula, it depends in the nature of experiment including number of treatments, replications, locations and study factors

Formula- 1: % germinated seed=(number of germinated seed/number of total seed)*100. Formula-2: Calculate your tray size (say, it is 1 m x 2 m) and spacing for transplanting (say, it is 20 cm x 20 cm). You need to use = (100 cm x 200 cm)/(20 cm x 20 cm)= (5 x 10)=50 germinated seed.

Have a good day

Hello, count 3 times 500 seeds and then weight them and use average, after by weight you can understand the approx. number.

Good luck!

Thank you all. I dont need to replant them. just a lab scale experiment on the quality of my liquid fertilizer. I was just going to keep one tray for control and one tray for liquid fertilizer. would it be fine to just add 50 seeds and pick the ones that germinate properly?

If your research question is to ask how well seedlings respond to your growth media (comparing presence and absence of fertilizer) then you had better use healthy seedlings. The other experiment would be to look at the effect on germination but these should be done separately. Consult a statistician regrding the number required and the method of analysis.