A cold frame is a low glass-topped box that warms soil early and shelters young plants from frost. The lid angle matters: a steeper lid sheds rain and catches more low winter sun, while a shallow lid suits taller crops. This free planner takes your frame size and lid angle, and works out frame area, back height rise, and how many plants fit inside.
What this tool does
This free cold frame layout planner runs entirely in your browser. Nothing you type is sent to a server, and nothing is stored online. You open the page, enter your own measurements, and the plan appears at once, with a simple drawing of the layout below the result. You can try again as often as you like, which makes it easy to test a bigger or smaller layout before you buy soil, pots, or timber. A short plan like this beats guessing, because a garden built on guesses often wastes space, water, and plants in the first season.
How to use it
Start by measuring the real space you have, not a rough guess: length, width, and height in the same units. Enter those numbers in order, then press the calculate button and read every result line, not just the total. If a line looks wrong, change one input at a time and run the tool again, so you can see exactly which input moved the result. Check the drawing too, because it shows whether the layout fits the space you measured. Save or copy the final numbers before you shop, while they are fresh.
Reading your result
The result lines break the plan into parts, so you can check each part against your space and your budget. A total alone rarely tells the full story, but a total built from visible parts does. If a result surprises you, trust the maths first and check your inputs second: most garden surprises come from a mistyped number, mixed units, or a measurement taken from the wrong side of a bed or sill. Fix the input, not the plan, and run it again.
Worked example
Try a frame 2 metres long and 1 metre wide, with a 30 degree lid angle and 12 plants per square metre. The area is 2 square metres. The back rise is half the width times the tangent of 30 degrees, about 0.29 metres. Plants that fit are 2 times 12, which is 24. That is a full spring sowing in a box you can lift with one hand.
Why this matters for a gardener
Cold frames stretch the season at both ends. Seedlings started inside a frame grow weeks ahead of outdoor sowings, and tender salads survive light frosts that would kill them in the open. Planning lid angle and plant count first stops a frame that is too low for its crops, or too crowded to vent. A planned frame also teaches venting discipline, which is the skill that keeps plants alive on sunny days.
Gardening tips
Face the lid toward the midday sun, and prop it open a little on any sunny day, even in winter, or plants can cook by noon. Close it before dusk to hold the heat. Water in the morning so leaves dry before night. Harden plants off by opening the lid wider over a week before moving them outside.
Common questions
Is this tool really free? Yes. It runs in your browser, needs no account, and has no sign-up step. You can use it as often as you like, for as many garden plans as you like.
Is the result exact for my garden? No. It is a planning estimate from the numbers you enter. Sun, wind, drainage, and local frost dates also affect real results, so check those on site before you build or plant.
Who is it made for? Home gardeners, balcony growers, and small-space growers who want a clear plan before they spend money on soil, pots, or timber.
Spanish version: Diseño de Semillero FrÃo Para Cultivar Todo el Año