Most coco grow bags are 100 cm long and come in widths of 15 to 24 cm and hydrated heights of 10 to 20 cm, which puts them between 15 and 40 litres. A 100 x 15 x 10 cm bag holds 15 litres and is the standard strawberry format. A 100 x 20 x 10 holds 20 litres. Tomato, cucumber and pepper growers mostly use 100 x 18 x 15 (27 L) or 100 x 20 x 15 (30 L) with three plants per bag. Pick the size from your target litres per plant and your row spacing, not from the catalogue.
This page is about sizing and layout. What a bag is, the pith and chip blends, film gauges and the wetting-up routine are in coco coir grow bags explained, and whether you should buy bags at all rather than loose blocks is on grow bags vs blocks.
Compressed vs expanded: the two sets of dimensions
Every coir bag has two sizes. The compressed slab inside the sleeve is 3 to 4 cm thick. Supplier listings describe slabs of 100 x 15 x 3 cm or 100 x 18 x 4 cm that swell to 100 x 15 to 20 x 10 to 15 cm once wet. Retail tomato bags quote expansion of roughly 4:1 to 5:1 from the compressed state.
The sleeve is made to the expanded size, so the slab you unpack rattles around in a bag that looks far too big for it. That's normal. It also means the number printed on the bag is almost always the hydrated volume, while the compressed thickness decides how many bags fit on a pallet.
Volume is just length x width x height in centimetres divided by 1,000. Run that check on every quote. Some listings pair compressed dimensions with a hydrated volume, and a few give volumes the dimensions can't hold. One exporter lists a 100 x 20 x 10 cm bag at 20 litres, which is right. If you see 100 x 15 x 10 sold as 18 litres, somebody is describing a different bag.
Common sizes in litres
| Hydrated size (cm) | Litres | Compressed thickness | Usual job |
|---|---|---|---|
| 50 x 18 x 15 | 13.5 | ~3 cm | Half slabs for short rows and odd lengths |
| 50 x 24 x 15 | 18 | ~3 cm | Half slabs, wider gutters |
| 100 x 15 x 10 | 15 | ~3 cm | Strawberry tabletops |
| 100 x 15 x 12 | 18 | ~3 cm | Retail tomato bags, strawberries |
| 100 x 20 x 10 | 20 | ~3 cm | Strawberries, low-volume tomato |
| 100 x 18 x 15 | 27 | ~4 cm | Tomato, cucumber, pepper |
| 100 x 20 x 15 | 30 | ~4 cm | Tomato, cucumber, pepper |
| 100 x 20 x 18 | 36 | ~4 cm | Retail tomato bags, long-season crops |
| 100 x 20 x 20 | 40 | ~4 cm | High-wire cucumber, two-stem pepper |
| 120 x 20 x 12 | 29 | ~3 cm | 120 cm gutter modules |
Compressed thickness varies with blend and press, so treat the column as a guide and ask for the real figure. A chip-heavy slab compresses less than pure pith.
Strawberry bags sit outside this grid. Specialist soft-fruit bags run 10 to 16 cm high and hold 14 to 26 litres per linear metre, which is a wide range for what looks like the same product. The height is what moves the volume at a fixed width.
Plants per bag and per metre
Three tomatoes, three peppers or two cucumbers per metre bag is the rule of thumb in hobby guides. Commercial growers work the other way round. They fix a plant density per square metre of greenhouse, then divide by the row spacing to get plants per metre of gutter.
Plants per metre of gutter = target plants per m² x row spacing in metres.
At a 1.6 m row spacing, 2.5 plants per m² is 4 plants per metre, so four per 100 cm bag or three per bag with a gap between bags. At 1.54 m rows, 4, 5 and 6 pepper plants per metre bag work out to 2.6, 3.25 and 3.9 plants per m².
| Crop | Density growers run | Plants per 1 m bag | Stems per m² | Notes |
|---|---|---|---|---|
| Tomato | 2.5 plants per m² | 3 to 4 | about 5 | Extra stems added in summer rather than extra plants |
| Cucumber, umbrella | 1.2 to 1.8 plants per m² | 2 to 3 | same as plants | Short crops, several plantings a year |
| Cucumber, high-wire | 1.9 to 2.5 plants per m² | 3 to 4 | 3 to 5 | Density pushed to 4 stems per m² under summer light |
| Sweet pepper | 2.6 to 3.9 plants per m² | 4 to 6 | 6 to 8 | Two stems per plant. Higher density paid better in coir bag trials |
| Strawberry | 8 to 13 per metre | 8 to 13 | n/a | Pre-cut holes fix the count. Troughs let you vary it |
| Herbs | Set by harvest method | Varies | n/a | See the herbs note below |
Pepper trials in 1 m coir bags found more plants per metre gave more fruit per square metre and better economics even as fruit per plant fell, and the authors suggested testing beyond 6 per metre. For cucumbers, density of 3 to 4 stems per m² was needed to reach the yield potential of high-wire systems, against roughly 1.2 to 1.8 plants per m² under umbrella training.
Herbs are the awkward one. Basil, coriander and mint are sometimes grown in slabs, but the plant count depends on whether you cut-and-come-again or lift whole plants, and on the pot or plug size. There is no standard figure worth quoting. If you're planning herbs in bags, the layout decisions are in growing herbs in coco coir.
Litres of coir per plant
This is where opinions diverge most, so here is the spread.
| Crop | Litres per plant in practice | Where the range comes from |
|---|---|---|
| Tomato | 4 to 10 | No yield difference between 5, 7.5 and 10 L when irrigated five times a day. At one irrigation a day, 5 L plants had more blossom end rot. Cutting from 3.75 to 2.5 L per plant cost little yield in a separate trial |
| Cucumber | 7 to 13 | Works out from 27 to 40 L bags carrying 2 to 3 plants. Fewer plants per bag than tomato because of the root mass |
| Pepper | 8 to 12 | 1 m x 22 x 22 cm coir bags (about 48 L) carried 4 to 6 plants in trials, so 8 to 12 L each |
| Strawberry | 1 to 3.3 | 2 L per plant is the published minimum. Below that root growth and yield fall |
The pattern is the same everywhere. Volume per plant barely affects yield when irrigation is frequent and even. It matters a lot when irrigation is infrequent or fails. A small bag is a bet on your drip system. A big bag is insurance you pay for in freight and coir.
Two ways to use that:
- If your controller fires on radiation sum and you have a dripper per plant, 5 to 7 litres per tomato is enough. A 20-litre bag with three plants is fine.
- If you irrigate on a timer a few times a day, or you grow where a pump failure means two hours in the sun, go to 9 to 10 litres per plant and a 27 to 30 litre bag.
How slab height and width change the water buffer
Two bags with the same volume don't behave the same. Water in a coir slab drains until the pull of gravity balances the pull of the coir pores, so the bottom few centimetres sit near saturation and the top dries out first. That saturated layer is roughly the same depth whatever the slab shape.
- Low, wide slab (100 x 20 x 10). A larger share of the slab is in the wet zone. More water held, less air, slower dry-back. Good for infrequent irrigation and cool climates, risky for pith-only blends under heavy drip.
- Tall, narrow slab (100 x 15 x 15 or 100 x 18 x 15). More of the slab sits above the wet zone. Faster dry-back, more air at the root crown, and a wider band of water content to steer with. Taller containers drain better at the same volume, which is why strawberry guides prefer a 10 cm or deeper profile even at 2 litres per plant.
Stonewool slab makers publish water content control ranges of 45 to 80 percent for 10 cm tomato slabs and 50 to 80 percent for 7.5 cm slabs. Coir runs wetter than stonewool at the same height and has no published equivalent, but the shape logic carries over. If you want to steer a crop generatively by letting the slab dry back between cycles, you need height. If you want a forgiving bag for a low-tech house, you want width.
Blend changes this as much as geometry. A 50:50 pith and chip slab at 10 cm can hold less water than a pure pith slab at 15 cm. Decide the dry-back you want first, then pick height and blend together.
Dripper placement and drain holes
Dripper and drain positions decide how the water moves through the slab. Get them wrong and the same bag behaves like two different products.
Drippers. One per plant is the working standard for fruiting vegetables. Strawberry growers typically run four drippers on a metre bag, some five, at 1.2 to 2 litres per hour each. Two per bag is the minimum for even wetting of any slab. Size the shot to the volume each dripper serves, not to the whole bag.
Drain slits. Cut them only once the slab is fully saturated and has sat wet for at least 24 hours. Stonewool guidance, which coir growers follow closely, puts the first drain hole at the lowest point of the slab in the direction of the gutter's slope, one drain point per 133 cm of slab, and at least 20 cm from the nearest dripper. The further the drain is from the dripper, the more of the slab refreshes with each cycle. Never cut directly under a plant block or dripper, and make the opening about 2 to 3 cm so it doesn't block. Cut upwards from the base.
How many. More drain holes make the slab drier and harder to resaturate. It's easier to add a slit mid-crop than to close one, so start with one per bag on a well-levelled gutter and add a second only if the far end stays wet. On an uneven gutter you'll need extra holes once the bags have settled.
Drain target. Soft-fruit growers in coir aim for 20 to 30 percent of applied water as drain to keep salts moving. Vegetable growers run similar numbers. If you're not getting drain from both ends of a 1 m bag, the slits are in the wrong place or the gutter isn't level.
Matching bag size to gutter and row layout
Bags are 100 cm for a reason: hanging gutters and ground troughs come in metre modules, and a metre bag with pre-cut holes lands plants at known positions for the dripper lines. A few things to check before you order:
- Gutter width. The hydrated bag must sit flat inside the gutter without riding up the sides. A 20 cm bag in an 18 cm gutter folds and drains unevenly. Measure the gutter floor, not the rim.
- Gutter length. Count how many full bags fit end to end and whether you want 50 cm half slabs to finish the row rather than a gap.
- Slope. Gutters are laid with a fall to a drain point. Bags on a slope shed water to the low end, so the drain slit and the position of the last dripper are set by the slope direction.
- Support wires. On coir bags for peppers, tying support wires to the bag can lift it and split the slab into compartments. Tie to the gutter or a crop wire instead.
- Hole spacing vs plant positions. A bag with three holes at 33 cm centres will not give you four plants per metre. Decide plant density first and have the holes cut to match, or buy bags with film-only holes you cut yourself.
- Bench vs ground. Tabletop strawberry systems at 70 to 100 cm height are built for 15 to 20 cm wide bags. Wider bags overhang and tip.
If you're moving from stonewool, note that stonewool slabs are 7.5 to 10 cm high and your gutters may be sized for them. A 15 cm coir bag can need a different gutter or a different clip.
What to specify when ordering
Put the hydrated dimensions and the expanded volume on the order together, so the factory can't satisfy one without the other. The full spec table is in the grow bags article; the items that matter for sizing are:
| Item | Why it matters for size |
|---|---|
| Hydrated L x W x H in cm | Fixes the volume and whether the bag fits the gutter |
| Expanded volume in litres | Catches a slab pressed too thin or too short |
| Fill weight per bag (dry, with moisture content) | Two bags with the same dimensions and different fill weights expand to different heights |
| Compressed thickness | Pallet count and freight |
| Blend and chip screen size | Sets how high the slab expands and how wet it runs |
| Plant hole count, size and spacing | Match to plants per metre and dripper layout |
| Dripper hole count and position | One per plant, placed so the drain is 20 cm or more away |
| Drain slits: pre-cut or not | If pre-cut, say which end and how far up the side |
| Film colour and UV life | White outside for hot houses, rated for as many seasons as you'll run the bag |
Ask for a sample of each size, hydrate it on a level bench, and measure. Hydrated height and volume are the two numbers that most often come in under spec.
We make grow bags and open-top bags to custom dimensions and blends from coir pith that's washed with water to lower EC and left unbuffered. If you have a gutter width, a plant density and a crop, send them over and we'll suggest a size to sample.
FAQ
What is the standard coco grow bag size?
The most common greenhouse bag is 100 cm long. Strawberry bags are usually 100 x 15 x 10 cm (15 litres). Tomato, cucumber and pepper bags are usually 100 x 18 x 15 cm (27 litres) or 100 x 20 x 15 cm (30 litres). Retail garden-centre bags run 100 x 15 x 12 to 100 x 20 x 18 cm.
How many litres is a 100 x 20 x 10 cm coco slab?
Twenty litres. Multiply length, width and height in centimetres and divide by 1,000. The same bag ships compressed to about 3 cm thick, so its volume in the box is only 6 litres before hydration.
How many tomato plants fit in a 1 metre coco bag?
Three is the usual number, four if you're running 2.5 plants per m² at 1.6 m row spacing with bags end to end. Trials found no yield difference between 5 and 10 litres of coir per plant under frequent irrigation, so a 20-litre bag with three plants works if your drip is reliable. Go to 27 to 30 litres if it isn't.
How many cucumber plants per slab?
Two per metre bag under umbrella training, three to four under high-wire where growers run 3 to 4 stems per m². Cucumbers build more root mass than tomatoes, so they're usually given 27 to 40 litre bags and more volume per plant.
How many strawberry plants per metre of grow bag?
Eight is the common retail count on a 15-litre bag. Commercial soft-fruit bags carry anything from 8 to 13 plants per metre. Two litres of coir per plant is the published minimum, which puts the floor at about 7 plants on a 15-litre bag and 10 on a 20-litre bag.
Where should drain holes go in a coco grow bag?
At the lowest point of the bag in the direction of the gutter slope, at least 20 cm from the nearest dripper and never under a plant or dripper. One drain point per bag is enough on a level gutter. Cut upwards from the base once the slab has been saturated for a day, and make the opening 2 to 3 cm.
Is a taller or wider slab better?
Taller slabs dry back faster and give you more room to steer water content. Wider, lower slabs hold more water and are more forgiving under infrequent irrigation. At the same volume, height drains better, so pick height for high-tech drip and width for low-tech houses.
Does the bag volume include the compressed or expanded coir?
Almost always the expanded, hydrated volume. The compressed slab is 3 to 4 cm thick and expands roughly four to five times. Check that the stated litres match length x width x height of the hydrated size, and ask for the fill weight so two bags of the same dimensions expand the same way.