Seed Tray & Cell Count Calculator

Why You Cannot Just Count Cells

If you want 72 tomato seedlings, sowing exactly 72 cells almost guarantees a shortfall. Two things eat into your count: not every seed germinates, and not every sprout survives transplanting. A typical fresh-seed germination rate is 80 to 90 percent, and transplant survival often runs 85 to 95 percent depending on how gently you pot up. Stack those together and a single seed per cell at 85 percent germination and 90 percent survival yields only about 77 usable plants per 100 cells.

How the Math Works

This calculator works backward from the number of plants you actually want. It accounts for sowing more than one seed per cell, which sharply raises the odds that at least one sprouts in each cell, then thins to the strongest.

per-cell success = 1 - (1 - germ%)^seedsPerCell
cells = ceil(target / (per-cell success x survival%))
trays = ceil(cells / cells-per-tray)

Picking a Tray Size

Standard 1020 trays come in common densities: 72-cell for veggies and flowers, 128-cell plug trays for high-volume starts, and 32- or 18-cell jumbo trays for plants that hate root disturbance like squash and cucumbers. Bigger cells mean fewer per tray but stronger, longer-lived seedlings. If you sow two seeds per cell at 85 percent germination, your odds of an empty cell drop from 15 percent to roughly 2 percent, so you can confidently fill far fewer cells to hit the same target.

Frequently Asked Questions

Should I sow one seed per cell or two?

Two seeds per cell is the safe default for most home gardeners, especially with older or bargain seed. It dramatically reduces empty cells, and you simply snip the weaker sprout at the soil line once both are up so you do not disturb the keeper's roots.

Where do I find my germination rate?

Seed packets usually print a germination percentage and a packed-for year. Fresh seed from a reputable supplier is often 85 to 95 percent, while seed more than two or three years old can drop well below 70 percent. When in doubt, run a quick paper-towel germination test on ten seeds.

What counts as transplant survival?

It is the share of healthy sprouts that make it through potting up or moving to the garden. Gentle handling, hardening off, and avoiding root-bound cells keep this above 90 percent. Rushed transplants, cold soil, or damping-off can pull it down toward 70 percent.

Why does the calculator round up to whole trays?

You cannot buy a fraction of a tray, so it rounds cells up to the next full tray and shows the spare cells you will have. Those extras are useful as backups or for succession sowing a week or two later.

Common Tip Percentages

Service	Typical Tip Range	Notes
Restaurant (sit-down)	15–20%	20%+ for exceptional service
Food delivery	10–20%	Consider extra for long distances
Taxi / rideshare	10–20%	More for assistance with luggage
Hotel housekeeping	$2–5/night	Leave daily, not just at checkout
Barber / hair salon	15–20%	On pre-discount total
Pizza delivery	10–15% or $3–5 minimum	Higher in bad weather

General Household Budget Ratios (50/30/20 Rule)

Category	% of Net Income	Examples
Needs	50%	Rent, groceries, utilities, insurance
Wants	30%	Dining out, entertainment, hobbies
Savings / Debt	20%	Emergency fund, retirement, extra payments

Common Measurement Conversions for Everyday Use

Quantity	US / Imperial	Metric Equivalent
1 cup	8 fl oz	237 mL
1 pint	16 fl oz	473 mL
1 quart	32 fl oz	946 mL
1 gallon	128 fl oz	3.785 L
1 lb	16 oz	453.6 g
1 ft	12 in	30.48 cm