Work out the volume you want to fill in litres, multiply by the share of coir in your mix, then divide by what one brick gives you. For planning, count a 5 kg block as 60 litres and a 650 g briquette as 8 litres of loose, hydrated coco peat. Those are the low ends of the usual ranges, so they leave you a margin. A 5-gallon pot of straight coir takes about 19 litres, which is about a third of a block or 2 to 3 briquettes.
The rest of this page is the arithmetic for each job, with the working shown so you can swap in your own numbers.
What one block or briquette gives you
| Format | Litres you'll usually get | Range you'll see quoted | Planning figure |
|---|---|---|---|
| 5 kg block | 60–75 L | about 50–100 L | 60 L |
| 650 g briquette | 8–9 L | 6.5–11 L | 8 L |
The spread is real, not sloppy labelling. Fine pith packs denser and expands less than pith with short fibre in it. Fast flooding expands less than slow soaking. And the biggest factor is measurement: loose, freshly fluffed coir reads much higher than coir that's been tapped down or left to settle in the pot. The reasons are covered in the coco peat blocks guide and, for small bricks, in using briquettes for propagation.
Moisture moves the number too. Only the dry coir expands, so a block delivered at 25% moisture holds about half a kilogram less coir than one at 15%, which is roughly 8 litres less medium.
How much margin? Planning on 60 L and 8 L already covers most of the variation. Add about 10% on top for spillage, overfilling trays and topping up pots after the first watering settles the medium. The best margin is one test: hydrate a block, fluff it, and count how many buckets of a known size it fills. Then plan with your own figure.
How much your containers hold
Pots sold in gallons
Fabric grow bags and retail pots labelled in gallons are usually close to real US gallons (3.785 L). Nursery trade pots are not. A "#1" or "1-gallon" nursery container is a size class, and the US nursery trade standard allows a range of volumes in each class.
| Label | Volume | Pots per 5 kg block (60–75 L) | Briquettes per pot (8–9 L) |
|---|---|---|---|
| 1 US gal (real) | 3.8 L | 15–19 | about 0.5 (2 pots per briquette) |
| 3 US gal | 11.4 L | 5–6 | 1.3–1.4 |
| 5 US gal | 18.9 L | 3–4 | 2.1–2.4 |
| 7 US gal | 26.5 L | 2 | 2.9–3.3 |
| 10 US gal | 37.9 L | 1.6–2.0 | 4.2–4.7 |
| Nursery #1 | 2.5–4.1 L | 14–30 | 0.3–0.5 |
| Nursery #3 | 10.3–12.2 L | 4–7 | 1.1–1.5 |
| Nursery #5 | 12.9–20.4 L | 2–5 | 1.4–2.6 |
| "4-inch" or quart pot | 0.84–1.03 L | 58–89 | 7–10 pots per briquette |
These are for 100% coir. If coir is only part of your mix, see step 4.
Worked example: ten 5-gallon fabric pots of straight coir need 10 × 18.9 = 189 L. Plus 10% is 208 L. At 60 L per block that's 3.5 blocks, so buy 4. In briquettes, 208 ÷ 8 = 26.
Pots sold in centimetres
A pot sold by its rim diameter tells you little about volume, because taper and depth vary so much. You can estimate it two ways.
The cylinder figure is the most a pot of that diameter and height can hold: volume (L) = 3.14 × radius² × height ÷ 1,000, all in cm.
| Pot (rim diameter = height) | Cylinder maximum | Pots per block (60–75 L) | Pots per briquette (8–9 L) |
|---|---|---|---|
| 10 cm | 0.8 L | 76–95 | 10–11 |
| 15 cm | 2.7 L | 22–28 | about 3 |
| 20 cm | 6.3 L | 9–11 | 1.3–1.4 |
| 25 cm | 12.3 L | 5–6 | 0.7 (1.5 briquettes per pot) |
| 30 cm | 21.2 L | about 3 | 0.4 (2.4–2.7 per pot) |
| 40 cm | 50.3 L | 1.2–1.5 | 6 briquettes per pot |
The tapered figure is closer to the truth. For a pot with top diameter D, base diameter d and height h, volume = 3.14 × h ÷ 12 × (D² + D × d + d²) ÷ 1,000. Take a pot 20 cm across the top, 15 cm across the base and 18 cm deep: 3.14 × 18 ÷ 12 × (400 + 300 + 225) ÷ 1,000 = 4.4 L. A straight-sided 20 × 18 cm cylinder would be 5.7 L, so the taper takes off nearly a quarter. The quickest check of all is to fill one pot with water from a measuring jug.
Raised beds and soil amendment
A bed's volume is length × width × depth. In metres, multiply by 1,000 to get litres. In feet, multiply cubic feet by 28.3.
There are two different jobs here. Filling a bed from scratch with a soilless mix uses a lot of coir. Working coir into existing soil uses far less. Common rates are one-third coir in a bed fill, and 1 part hydrated coir to 6–8 parts soil worked into the top 15–20 cm when amending. The reasoning behind those rates is in coco coir in soil and raised beds.
| Job | Volume | Coir share | Coir needed | 5 kg blocks (60–75 L) |
|---|---|---|---|---|
| Fill 2.4 × 1.2 × 0.3 m bed | 864 L | one-third | 288 L | 3.8–4.8, buy 5 |
| Fill 4 × 8 ft bed, 12 in deep | 32 cu ft = 906 L | one-third | 302 L | 4.0–5.0, buy 6 for margin |
| Fill 4 × 4 ft bed, 6 in deep | 8 cu ft = 227 L | one-third | 76 L | 1.0–1.3, buy 2 |
| Amend 1 m², 15 cm deep | 150 L of soil | 1:8 to 1:6 | 19–25 L | about a third of a block |
| Amend 1 m², 20 cm deep | 200 L of soil | 1:8 to 1:6 | 25–33 L | about half a block |
| Amend 10 m², 20 cm deep | 2,000 L of soil | 1:8 to 1:6 | 250–333 L | 3.3–5.6, buy 6 |
Notice the jump. Filling one 4 × 8 ft bed takes about as much coir as amending 10 m² of ground.
Seed trays and plug trays
For an open seed tray, multiply the tray's inside area by the fill depth. A standard 1020 tray is about 25.4 × 50.8 cm, or 1,290 cm².
| Tray and fill | Litres per tray | Trays per briquette (8–9 L) | Trays per block (60–75 L) |
|---|---|---|---|
| 1020 tray, 1.3 cm deep | 1.7 L | 4–5 | 35–44 |
| 1020 tray, 2.5 cm deep | 3.2 L | 2–3 | 18–23 |
Plug trays are the awkward one, because cell volume varies a lot between makers, and between square, round and deep cells with the same cell count. Litres per tray = number of cells × ml per cell ÷ 1,000.
| Plug tray | Cell volume seen in catalogues | Litres per tray | Trays per briquette (8–9 L) |
|---|---|---|---|
| 288-cell | 6–13 ml | 1.7–3.7 L | 2–5 |
| 200-cell | 11–23 ml | 2.2–4.6 L | 1–4 |
| 128-cell | about 25 ml | 3.2 L | 2–3 |
| 72-cell, shallow round | about 22 ml | 1.6 L | 5 |
Deep 72-cell forestry and vegetable trays hold several times the shallow figure, so read the cell volume off the tray's spec sheet. A worked example: 10,000 transplants in 128-cell trays is 10,000 ÷ 128 = 79 trays. At 25 ml a cell that's 250 L, plus 10% is 275 L, or 4.6 blocks. Buy 5.
Greenhouse slabs per hectare
If you buy ready-made grow bags or slabs, you count bags rather than litres. Work from plant density.
Bags per hectare = plants per m² × 10,000 ÷ plants per bag.
Tomatoes at 2.5 plants per m² mean 25,000 plants per hectare. At three plants per 1 m bag that's 8,333 bags. At four per bag it's 6,250, which is also the metres of row in a hectare at 1.6 m row spacing (10,000 ÷ 1.6), so the bags run end to end.
| Tomato layout | Bags per ha | Bag size | Coir volume per ha |
|---|---|---|---|
| 3 plants per bag | 8,333 | 27 L (100 × 18 × 15 cm) | 225,000 L |
| 4 plants per bag | 6,250 | 20 L (100 × 20 × 10 cm) | 125,000 L |
If you fill troughs or buckets from blocks instead, divide the litres by 60–75. The 125,000 L layout is 1,667–2,083 blocks. Bag dimensions, plants per bag for other crops and litres per plant are in grow bag sizes and plant density.
Container nurseries per acre
Nursery production is usually planned by containers per acre, with walkways and roads already allowed for. Typical figures are 20,000–22,000 #1 containers per acre, or about 7,700 #3 containers. Multiply by the class volume, then by the coir share of your mix. A bark-based mix at 4 parts bark to 1 part amendment is common, which makes coir 20% of the volume.
| Containers per acre | Mix per acre | Coir at 20% | 5 kg blocks |
|---|---|---|---|
| 20,000–22,000 × #1 (2.5–4.1 L) | 50,000–90,000 L | 10,000–18,000 L | 133–300 |
| 7,700 × #3 (10.3–12.2 L) | 79,000–94,000 L | 15,800–18,700 L | 211–312 |
For a hectare, multiply by 2.47. For a straight coir mix, multiply the block count by five.
Lay-flat polybags, common in fruit and forestry nurseries, are sold by flat width and height. Filled, a bag of flat width W becomes a cylinder about 2W ÷ 3.14 across. A 15 × 20 cm bag fills to about 9.5 cm diameter, so 3.14 × 4.8² × 20 ÷ 1,000 = 1.4 L if filled to the top. That's 42–52 bags per block of straight coir.
Adjust for your mix
Most growers don't use straight coir. The coir you need is the mix volume × the coir share.
| Mix (by volume) | Coir share | Coir for one 5-gallon pot (18.9 L) | Coir for a 2.4 × 1.2 × 0.3 m bed (864 L) |
|---|---|---|---|
| 100% coir | 100% | 18.9 L | 864 L |
| 70 coir : 30 perlite | 70% | 13.2 L | 605 L |
| 2 coir : 1 perlite : 1 vermiculite | 50% | 9.5 L | 432 L |
| 50 coir : 50 perlite | 50% | 9.5 L | 432 L |
| Coir, vermiculite, compost in thirds | 33% | 6.3 L | 288 L |
| 4 bark : 1 coir | 20% | 3.8 L | 173 L |
Two things catch people out. First, measure the coir after it's hydrated and fluffed, not as dry compressed brick, or the ratio comes out wrong. Second, blended media often come out a little short of the sum of their parts once fine particles settle into the gaps between coarse ones, and again after the first watering. Mix one batch, fill a known container, and adjust before you scale up. Ratios for different crops are in coir, perlite and vermiculite mixes.
A quick checklist
- Litres per container, from the tables above or a jug of water.
- × number of containers.
- × coir share of the mix.
- 10% for waste and settling.
- ÷ 60 for 5 kg blocks, or ÷ 8 for 650 g briquettes, then round up.
Once your first block is hydrated, replace 60 or 8 with what you actually measured. If you're working out a larger order of blocks, briquettes, grow bags or a custom blend, send us your container sizes and counts and we'll work through the quantities with you.
FAQ
How many litres does a 5 kg coco peat block make?
Usually 60 to 75 litres of loose, hydrated coco peat, though you'll see anything from about 50 to 100 litres quoted. The difference comes from the grade, how slowly it was soaked and whether the volume was measured loose or settled. Plan on 60 litres until you've measured one yourself.
How much coco peat do I need for a 5-gallon pot?
A 5 US gallon pot holds about 19 litres. In straight coir that's roughly a third of a 5 kg block, or 2 to 3 briquettes of 650 g. With a 70:30 coir and perlite mix you need about 13 litres of coir per pot.
How many coco coir bricks do I need for a raised bed?
Work out the bed volume, take a third of it for a typical bed fill, and divide by 60 litres per 5 kg block. A 4 by 8 foot bed 12 inches deep holds about 906 litres, so a third is 302 litres, which is five to six blocks. Amending existing soil needs far less, about 25 to 33 litres per square metre at 20 cm deep.
How many seed trays does one coco peat briquette fill?
A 650 g briquette gives 8 to 9 litres. That fills two to three standard 1020 trays at 2.5 cm deep, or four to five at 1.3 cm. In plug trays it depends on cell size, from about two to five 288-cell trays.
Is a 1-gallon nursery pot really one gallon?
Not necessarily. Nursery pots are sold by size class, and a #1 container can hold anywhere from about 2.5 to 4.1 litres, while a real US gallon is 3.785 litres. Check the volume moulded into the base or fill one with water to be sure.
Should I measure coco peat before or after hydrating it?
After. Mix ratios and container volumes refer to loose, damp, hydrated coir. Compressed coir expands several times when wetted, so measuring dry brick throws every ratio off.
How much extra coco peat should I buy?
Plan with the low end of the yield range, 60 litres per block and 8 litres per briquette, then add about 10 percent for spillage and settling. For big jobs, hydrate one block first and measure what it actually gives before ordering the rest.