How to calculate your cost per tray, price a clamshell, and set a weekly tray target. Fix it from only $3 a month.

Step 1. Rule the sheet into 3 columns

Left column: the name of the line. Middle column: the unit that line is measured in. Right column: your number. Leave the right column empty until the figure is one you have actually looked up.

Give every row a unit before you write a single digit in it. A number with no unit beside it is the commonest error in this exercise, because two months later nobody remembers whether 1.50 meant grams, quarts, dollars or trays.

Date the top of the sheet. You will recalculate it, and two undated sheets are worse than one.

Step 2. List every input that touches one tray, then tally it

Work down the input rows and write one number per row. Where a sack, a roll or a case covers several trays, divide the paid price by the number of trays it covers before anything goes in the right column. That single habit repairs most of what growers get wrong here.

• Seed. Take the price per pound off the invoice, divide by 16 to get a price per ounce, then multiply by the ounces you weigh into one tray.
• Growing medium. Price of the bag, divided by the number of trays the bag fills. Fill 4 trays with it once and count, rather than trusting the number on the bag.
• Clamshells, labels and seals. Case price divided by the count in the case, then multiplied by the number of clamshells one tray fills.
• Water and power. If you have never measured this, put a modest round figure in your second pen color and move on. It is a minor row and it will not shift the answer far.
• Shelving and lamps. Purchase price divided by the number of trays the unit will carry before it needs replacing. Guess how long it lasts in months, multiply by trays a month, and use that as the divisor.
• Pitch or delivery fee. The weekly fee, divided by the number of trays you plan to shift that week.

Then add the column. Add it twice, once downward and once upward. Matching totals means you can stop. That is Subtotal A.

Step 3. Time yourself, and put the labor minutes on the sheet

Nobody enjoys this step and everybody leaves it out, which is why so many worksheets produce a price that seems healthy and pays nothing. Start the stopwatch when you pick the tray up and stop it when you put it down. Do it once for sowing, once for cutting, once for packing.

Write the 3 figures in the minutes rows and add them. If you sowed eight trays in one session, take the session total and divide by eight before the number goes on the sheet.

Now convert. Divide what you pay yourself per hour by 60 to get a per-minute figure, then multiply by the minutes altogether.

• $15 an hour is 25 cents a minute.
• $18 an hour is 30 cents a minute.
• $24 an hour is 40 cents a minute.

Write it down as Subtotal B. If you refuse to pay yourself anything, write zero, but write the minutes anyway. The minute count is what tells you later which crop is expensive to handle.

Step 4. Add the two subtotals to get the true cost of one tray

Subtotal A plus Subtotal B. That is the true cost of one tray, and it belongs in the box in bold.

Read back up the sheet once before you carry the answer forward, looking for a figure entered twice. Double counting is the usual explanation when a worksheet comes out overstated: the packing case gets counted in the clamshell row and again in the labels row, or the shelving row gets counted per tray and again per month.

Sanity test: if this figure came out under a dollar, you have divided somewhere you meant to multiply. Go back to the seed row and check the divisor.

Step 5. Convert to a cost per ounce, then to a cost per clamshell

Cut a tray and weigh it. Not a tray from a video, and not the number on the seed packet. Yours, on your scale, in ounces, after any trimming you would normally do.

Divide the true cost of one tray by that weight. The answer is your unit cost, expressed per-ounce, and it is the most portable figure on the whole sheet, because it lets you price a bag, a clamshell or a large delivery without redoing any of the work above.

Then multiply the per-ounce figure by the fill weight of a clamshell. That is what sits inside one clamshell before you have made a single cent on it. Write it in the row for the cost inside one clamshell.

Keep two decimals. Rounding at this row rather than at step 6 quietly moves the shelf price by a quarter or more once it is multiplied up.

Step 6. Choose a mark-up, multiply, and round to a sane shelf price

The mark-up is the only number on this sheet you choose rather than measure, so choose it against what it has to cover rather than a feeling.

Multiply the cost inside one clamshell by the multiplier you ticked. The answer will be an ugly figure. Round it, because ugly figures cost you buyers at a stall and cost you credibility on a price list.

Rule of thumb for the direction: round up whenever the gap is more than about a dime, round down only to reach a price point that is genuinely easier to say out loud. Never round down twice on the same sheet.

Write the rounded figure in the shelf price row. Then multiply it by the clamshells one tray fills, and write that in the row for what one tray returns.

Step 7. Work backwards from a monthly goal to a weekly tray number

Put the monthly figure you want the rack to return at the top of a fresh row. Not a wish. A figure you could name to somebody without flinching.

Subtract the true cost of one tray from what one tray returns. That difference is the contribution one tray leaves behind, and it is the only figure that divides cleanly into a goal.

1. Monthly goal divided by contribution per tray gives trays a month.
2. Trays a month divided by 4.33 gives trays a week.
3. Round the weekly answer up to a whole tray. You cannot sow part of one.

Use 4.33, not 4. A month is not four weeks. Dividing by 4 flatters the weekly answer by roughly eight percent, which is exactly the gap that leaves a schedule short.

Step 8. Subtract an allowance for the trays that fail

Sown is not the same as sold. Some trays go over, some come up patchy, some get knocked off a shelf. The weekly figure from step 7 assumes each tray makes it, so it needs correcting upward.

Write your allowance as a percent, then divide rather than multiply.

• Turn the percent into a decimal and subtract from 1. An eight percent allowance gives 0.92.
• Divide the weekly tray figure by that decimal.
• 24 divided by 0.92 is 26.1, so you sow 27.

Multiplying by 1.08 gives 25.9, which is not the same answer and is short every time. Dividing is the correct move, and the gap widens as the allowance rises.

Nothing to work from? Put 10 percent in the box in your second pen color, then count for one quarter and replace it with a measured figure. Logging each sowing in GLAP counts it for you, and the $0 tier holds 8 trays at once.

Step 9. Check the answer against what the shelving physically holds

The sheet has now produced a weekly tray number. It has no idea whether that number fits in your space, so this last step is the reality check.

1. Count the usable shelves. Count how many trays sit on one shelf. Multiply. That is what the rack holds at once.
2. Count the days a crop occupies a shelf, cleaning and refilling included. Divide 30 by that figure. That is your turns a month.
3. Multiply what the rack holds by the turns. That is the most trays a month the rack can deliver.

Compare that number with the adjusted weekly one from step 8, multiplied by 4.33. If the rack figure is the smaller of the two, the sheet is not telling you the goal is wrong. It is telling you which lever to pull.

Pull the cheap lever first. Revisit the multiplier in step 6 before you buy shelving. Reworking one box on a worksheet is free. A second rack, a second lamp and a second timer are not.