Seed spacing calculator
Choose a crop and give the size of your rows or bed. The calculator tells you how many plants fit, how many seeds to have ready, and draws the layout to scale.
How many will fit
Pick a crop and give your rows or your bed. The spacing fills in from RHS guidance, and you can change it to match your seed packet.
40 lettuce (hearting)
In a bed 3 m by 1.2 m: 4 rows along the length, 10 in each.
A square grid fits more here: 40 against 38 in staggered rows, because the shifted rows lose a plant at the end in a bed this size.
Have 120 seeds ready. Sown thinly along the row, then thinned. We allow three seeds for each plant you want.
RHS spacing for lettuce (hearting): 30cm (12in) along the row, 30cm (12in) between rows (RHS grow your own guide). Planted too close, hearting lettuces will not heart.
How to use it
Pick "A bed" for a raised bed or a block of ground, or "Separate rows" if you sow in rows along the plot. Give the sizes in metres or feet, then choose the crop. The spacing boxes fill in from RHS guidance. Seed packets vary, so change them to match yours, or pick "Something else" and type your own.
How to read the answer
The big number is how many plants fit. For a bed, the calculator tries two layouts. A square grid puts the plants in straight lines both ways. Staggered rows shift every other row half a plant along, like bricks in a wall, so the rows can sit a little closer while each plant keeps its full space. Staggering usually wins in wide beds; in narrow ones the shifted rows lose a plant at each end and the square grid fits more. You get whichever fits more, and it says which.
The seed figure allows for seeds that do not come up and for thinning, which means pulling out the extra seedlings so the rest have room. Our allowance: three seeds for each plant when you sow thinly along a row; two a module when you raise plants in trays; the number the RHS gives for each station (a station is one spot where you sow a small pinch); and one spare in ten for onion sets, garlic cloves, potatoes and big seeds such as beans.
How it is worked out
Each plant gets its own space, so the first and last plant sit half a spacing in from the edge. A 3 metre row at 30cm holds ten plants. The spacings come from each crop's RHS grow your own page, read in October 2026. Where the RHS gives a range we keep the range and start at its wider end, so plants get the full room; move it down for compact varieties. Where it gives no gap between rows, as for cabbages and tomatoes, we use the plant spacing both ways and say so. For peas the RHS sets rows as far apart as the plants grow tall, so we start at 60cm and you should check your packet.
For staggered rows, the gap between rows is worked out so that the nearest plant in the next row is still the full row spacing away. With the same spacing both ways, that brings the rows in to about 87% of the spacing.
More for the plot
For when to sow, see the vegetable planting calendar, and check the average frost dates before planting out anything tender.
Garden art prints to go with it
Questions people ask
How many plants can I fit in a 1.2 by 2.4 metre raised bed?
It depends on the crop. Hearting lettuces at 30cm each way fit 32; garlic at 15cm in the row with rows 30cm apart fits 64. Put your crop and bed size into the calculator for the exact figure.
Is staggered planting better than square?
Often, but not always. Staggered rows can sit a little closer together, so a wide bed fits more. In a narrow bed the shifted rows lose a plant at the ends and a square grid can fit more. The calculator works out both and shows the better one.
Why sow more seeds than I need plants?
Not every seed comes up, and slugs and birds take some seedlings. Sowing a few extra and thinning to the strongest gives you a full row. Our allowance is stated under the answer for each way of sowing.
Where do the spacings come from?
From each crop’s RHS grow your own page, read in October 2026. Where the RHS gives a range we start at the wider end. Seed packets differ by variety, so you can change the spacing.