Microgreen Seed Density calculator
Microgreen seed density calculator
Pick a crop and your tray size to get a sowing weight scaled to your actual tray not a fixed chart. Crops with inconsistent source data are shown as a range and flagged.
How this is calculated
Weight scales with tray area not the other way around so every crop's reference weight below is tied to a fixed baseline area (a standard 1020 tray's ~183 in² usable surface) and then scaled by the ratio of your chosen tray's area to that baseline. This is why the calculator asks for tray size before showing a result and why it doesn't use a single flat number per crop.
For the "other crop" mode the sowing target comes from the published density-per-area standard (6–8 seeds/in² for large seed, 10–12 seeds/in² for small seed, per Illinois Extension and Penn State Extension), converted to weight using the seeds per gram figure you provide.
Reference weights are drawn from Utah State University Extension's trial data, Johnny's Selected Seeds' 2017 microgreens yield trial and True Leaf Market product specs with CropKing's commercial chart used only where no extension or trial figure exists. Crops marked "wide range" have source figures that disagree by roughly 2× or more shown as a range rather than averaged since averaging would hide a real unresolved question (usually hulled vs hulls-on seed or harvest stage differences).
This microgreen seed density calculator converts a crop choice and your tray's real dimensions into an exact sowing weight in grams and ounces instead of asking you to eyeball a chart built for a different tray size.
It covers twenty common microgreens crops with built-in reference data plus a custom mode for anything else, and flags results where the underlying research disagrees.
If you've searched how much seed per tray microgreens actually need this gives a tray specific answer instead of a generic chart figure.
What the Microgreen Seed Density Calculator Does
Most seed density charts print one number per crop and leave you to guess how it changes once your tray isn't the standard size.
This calculator ties every crop's reference weight to a fixed baseline a standard 1020 tray's usable growing surface, about 183 square inches then scales that weight by the ratio of your tray's area to the baseline.
A half tray gets roughly half the seed; a larger flat gets proportionally more.
For crops not on the built-in list it switches to a published density per area standard instead: 6 to 8 seeds per square inch for large seeds like peas or sunflower, 10 to 12 for small seeds like brassicas numbers Illinois Extension and Penn State Extension both publish.
That rate converts to weight using the seeds per gram figure you supply since seed size varies enough between suppliers that a flat chart can miss badly.
How to Use the Microgreen Seed Density Calculator, Step by Step
Start by picking a crop under From the list. The calculator groups crops into three bands well documented, moderate range and wide divergence so you can see how solid the source data is before committing seed.
If your crop isn't listed, switch to Other / custom crop, choose large seed (peas, sunflower, beans, squash sized) or small seed (brassicas, herbs, lettuces) then enter seeds per gram for your variety.
If you don't know that number, count 25 seeds, weigh them on a gram scale and enter both figures into the built-in helper it works out seeds per gram automatically.
Next, set tray size: the standard 1020 usable surface for a figure adjusted for sloped tray walls, the standard 1020 nominal size for a flat 10x20 inch footprint or Custom tray for anything else.
For a custom tray, measure the actual growing surface not the outer rim and enter length and width in inches.
The result updates as soon as both dimensions are filled in giving you grams of seed per 10x20 tray or whatever size you've entered.
How to Read Your Results
The large figure at the top is your sowing weight in grams with the ounce equivalent beside it.
For crops with a seeds per ounce figure: pea shoots, sunflower and broccoli among them you'll also see an approximate seed count, useful if you buy seed by the thousand rather than by weight.
Below that an info grid pulls three details from extension and trial sources: presoak time, days of blackout before light and total days to harvest.
If your crop falls into the moderate range or wide divergence group, a flagged note explains why usually a harvest stage difference between trials or a real disagreement between hulled and hulls-on seed data.
A scale note at the bottom shows the 183 square inch reference area, your actual tray area and the multiplier between them which is the fastest way to check a result against any microgreens seed density chart you've seen elsewhere.
Who the Microgreen Seed Density Calculator Is Built For
Hobby growers running one 10x20 tray on a counter get a precise number without doing area math themselves.
Market growers working mismatched tray sizes: half trays, deep flats, repurposed bakery trays get a way to scale seeding rates consistently instead of estimating by eye.
Anyone trying a crop outside the standard rotation from bull's blood beets to amaranth, gets a working number even without a dedicated microgreens seeding rate calculator built for that crop specifically.
Bulk buyers who think in seed count rather than weight get that conversion built in too.
Real World Use Cases and Practical Tips
Say you normally seed a full 1020 tray of radish but want to test a half tray first. Enter its actual dimensions under Custom tray and the calculator scales radish's reference weight down proportionally instead of eyeballing half of a number never meant to bend that way.
Or say you're growing amaranth for the first time and it isn't in your usual chart. Switch to custom crop mode, pick small seed for the 10 to 12 seeds per square inch rate, weigh a 25 seed sample to get seeds per gram and the calculator turns that into a seed count and weight together.
A few crops: buckwheat and sunflower especially have source figures that disagree by two to ten times usually from hulled versus hulls on seed weighing differently for the same count.
Where that's flagged, treat the figure as a starting point and adjust based on your own seed lot.
Frequently Asked Questions
How much seed should I sow per tray for microgreens?
It depends on the crop and your tray's exact area which is why one flat number rarely holds up across setups.
This calculator scales a documented reference weight to your tray's actual size so a full 10x20 tray and a quarter tray of the same crop get proportionally different weights. For crops without a documented reference weight it falls back to a seeds per area rate.
Why do some crops show a range instead of one number?
Because the underlying research disagrees with itself sometimes by a wide margin. Most disagreements trace back to seed lot differences hulled versus hulls on or harvest stage in the original trial data. Showing a range beats averaging two numbers that describe different things.
Can I use this for a tray that isn't the standard 10x20 size?
Yes. Select Custom tray, measure your growing surface's actual length and width in inches and every result scales to that area automatically most published density charts only cover the standard size.
What if I don't know my seed's weight per count?
Use the built-in helper under the custom crop tab. Count 25 seeds, weigh them in grams, enter both numbers and the calculator works out seeds per gram for you.
This microgreen seed density calculator exists because most seed density charts assume a tray you probably aren't using and because a handful of common crops have source data that genuinely disagrees.
Enter your crop and your real tray dimensions and you get a sowing weight scaled to that tray with a clear flag anywhere the underlying data isn't settled sowing by a number you can actually trust instead of a guess.Penn State Extension
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