Seed Starting Count Calculator

Enter Your Details

Target plants (final)

How many healthy plants you want at transplant time.

Enter a number from 1 to 100000.

Germination rate (%)

Typical sprout rate for your seed lot.

Enter a percent from 1 to 100.

Survival / transplant success (%)

Losses from damping-off, culling, and handling.

Enter a percent from 1 to 100.

Safety margin (%)

Extra buffer for surprises and selection.

Enter a percent from 0 to 200.

Seeds per cell/pot

Use 2+ when thinning is acceptable.

Enter a number from 1 to 10.

Cells per tray

Examples: 72, 128, 200, or 6-packs.

Enter a number from 1 to 1000.

Seeds per packet

Used to estimate packet purchases.

Enter a number from 1 to 10000.

Reset

Example Data

Scenario	Target	Germination	Survival	Margin	Seeds/Cell	Tray Cells	Seeds to Sow	Trays	Packets
Tomatoes for beds	24	85%	90%	10%	1	72	35	1	2
Herbs with thinning	60	75%	85%	15%	2	128	109	1	5
Flowers for borders	120	70%	80%	20%	1	72	258	4	11

Examples show how loss rates and safety margin change sowing needs.

Formula Used

Effective success rate

Effective Success = (Germination% ÷ 100) × (Survival% ÷ 100)

Seeds required before margin

Seeds Core = ceil(Target Plants ÷ Effective Success)

Seeds to sow with safety margin

Seeds to Sow = ceil(Seeds Core × (1 + Safety Margin% ÷ 100))

Cells, trays, and packets

Cells to Fill = ceil(Seeds to Sow ÷ Seeds per Cell)
Trays Needed = ceil(Cells to Fill ÷ Cells per Tray)
Packets Needed = ceil(Seeds to Sow ÷ Seeds per Packet)

Rounding uses ceiling so you do not under-sow. Expected usable seedlings are estimated as floor(Seeds to Sow × Effective Success).

How to Use This Calculator

Enter the final number of plants you want to transplant.
Set germination and survival based on past batches.
Add a safety margin if you want extra selection.
Choose seeds per cell and your tray cell count.
Submit to see seeds, cells, trays, and packets needed.
Use CSV or PDF buttons to save your planning record.

Practical Notes

For low germination lots, test 10–20 seeds first.
If you sow 2 seeds per cell, plan thinning time.
Survival varies with airflow, watering, and sanitation.
Use safety margin for staggered planting and backups.

Seed Success Assumptions

Accurate planning starts with realistic performance rates. Germination reflects seed viability and temperature control, while survival covers damping-off, weak seedlings, and transplant shock. Multiply these rates to estimate the chance that one seed becomes a plant you can set out. When either rate is uncertain, run a quick test sowing and adjust inputs.

Tray Planning and Space

The calculator converts required seeds into cells, then trays, so you can match indoor space and lighting capacity. Using more seeds per cell increases thinning work but can protect against empty cells in finicky varieties. Choose a tray size you actually own, and remember to include airflow gaps between trays for healthier foliage. Ensure lights cover every tray evenly.

Packets and Cost Control

Packet estimates prevent last-minute shortages and help budget planning. Seed counts per packet vary widely, especially for pelleted seed, hybrids, and coated treatments. If your packet listing is vague, weigh or count a small sample and update the average. Buying one extra packet can be cheaper than losing a planting window. Store leftover seed cool and dry, then revise packet counts next season using what you learned.

Timing and Succession Starts

Seed quantity is only useful when paired with schedule. Align sowing dates with your expected last frost, bed readiness, and hardening time. For long-season crops, a higher margin allows you to select the strongest seedlings and still keep replacements. For fast crops, smaller batches every one to two weeks improve harvest continuity. If daylight is low, start fewer plants or extend grow time to avoid stretching and weak stems.

Quality Checks Before Sowing

After calculating, confirm that your medium volume, labels, and watering approach match the planned cell count. Sanitize trays, use consistent depth, and track variety, lot, and date. If expected usable seedlings exceed targets by a lot, reduce margin or seeds per cell to avoid crowding and nutrient stress. Record actual germination and survival results after transplanting, so future calculations reflect your specific setup.

FAQs

1) What germination rate should I use?

Use a recent seed test, past notes, or the supplier’s typical range. If you are unsure, start conservative, then update the rate after a small trial sowing under your normal light and temperature.

2) How do I estimate survival or transplant success?

Think about losses from damping-off, slow growers, pests, and handling. If your setup is stable, 85–95% is common. New setups may be lower until watering and airflow are dialed in.

3) When should I sow two seeds per cell?

Use two seeds when germination is unreliable, seeds are tiny, or a full tray is critical. Plan to thin to the strongest seedling early to prevent competition and weak, stretched growth.

4) What safety margin is practical?

A 5–15% margin fits most home starts. Increase margin for slow or valuable crops, unpredictable weather, or when you want extra plants for selection and replacements.

5) How are trays calculated if I mix tray sizes?

Enter the tray size you will use most. If you mix sizes, calculate once for each tray type and split the cell count across them. This keeps the space plan realistic for your shelving.

6) Why can expected usable seedlings differ from my target?

Expected usable seedlings are an estimate using your rates, while seeds to sow are rounded up to avoid shortages. Small differences are normal. If the gap is large, reduce margin or refine your rates.