How Many Drip Zones Can My Supply Feed

How many drip zones can my supply feed? Divide total flow by measured supply flow and round up to the next whole zone. Total flow is emitters times emitter flow. If the result is 1.2 zones, you need 2 zones. If the result is 2.1 zones, you need 3 zones.

How Many Drip Zones Can My Supply Feed in Plain Words

A drip zone is one set of drip lines that runs at the same time from one valve. A supply is the flow your tap can deliver, in litres per hour or in gallons per hour. The zone count is the number of sets you must split a layout into so no set asks for more flow than the supply can give.

Start with total flow. Count every emitter in the whole layout, then multiply by the flow of one emitter. If that total fits inside supply flow, the layout needs one zone.

The Three Formulas

Three formulas give the zone count, using only figures you can count or measure before you buy parts.

First, total flow equals emitters times emitter flow. Use the same units on both sides. Do not mix litres per hour with gallons per hour in one calculation.

Second, zones equals ceil of total flow divided by supply. Ceil means round up to the next whole number. A result of 1.01 becomes 2 zones. A result of 2.0 stays 2 zones, because the total fits exactly. A result of 2.01 becomes 3 zones.

Third, emitters per zone equals supply divided by emitter flow. This gives the largest number of emitters one zone can run at the stated emitter flow.

The Verified Worked Example in Full

The verified example uses six 10 m rows with one line each, 30 cm emitter spacing and 2 L/h emitters. Each row gives 33 emitters, from floor of 10 divided by 0.30. Six rows give 198 emitters in total.

Total flow is 198 emitters times 2 L/h, which is 396 L/h. Supply flow is 1,000 L/h. Zones equals ceil of 396 divided by 1,000, which is 1 zone.

A 1,000 L/h supply can run about 500 emitters of 2 L/h, because 1,000 divided by 2 is 500. The example uses 198 emitters, so it uses less than half of that. The planner gives the tubing as about 66 m of tubing plus 10 percent spare, and the header length is not stated on the page.

Measure Your Supply Flow at the Tap With a Bucket

Supply flow is a measured figure, not a guess from pipe size. The planner page says supply flow can be measured at the tap with a bucket. That test gives the flow your tap can deliver in real use.

Put a bucket of known size under the tap, open the tap fully, and time how long it takes to fill. Divide bucket size by time in hours to get litres per hour. A 10 litre bucket that fills in 36 seconds is 1,000 L/h, in 72 seconds it is 500 L/h, and in 18 seconds it is 2,000 L/h.

Run the test at the tap you plan to use, with the same hose or fitting you plan to use, and with other taps closed. If flow falls when another tap opens, use the lower result. In imperial units, a 5 gallon bucket that fills in 60 seconds is 300 gallons per hour, and in 120 seconds it is 150 gallons per hour.

Zone Counts for Named Layouts in Litres Per Hour

The table below uses 2 L/h emitters for every layout, so total flow is emitters times 2. Other rows are example layouts worked through the same formulas. Only the row with 198 emitters is the verified planner example.

Layout	Emitters	Total flow (L/h)	Zones at 500 L/h	Zones at 1,000 L/h	Zones at 2,000 L/h
Small bed	60	120	1	1	1
Planner example, six 10 m rows	198	396	1	1	1
Medium rows	300	600	2	1	1
Large rows	500	1000	2	1	1
Very large rows	800	1600	4	2	1
Extra large rows	1200	2400	5	3	2

Read across from your layout, then down from your measured supply. A medium layout at 600 L/h needs 2 zones on a 500 L/h supply, but 1 zone on a 1,000 L/h supply. A very large layout at 1,600 L/h needs 4 zones on a 500 L/h supply and 1 zone on a 2,000 L/h supply.

The jump from 1 zone to 2 zones happens as soon as total flow passes supply flow. A layout at 1,010 L/h would need 3 zones on a 500 L/h supply, because ceil of 1,010 divided by 500 is 3. Ten extra litres per hour would add a whole zone.

Emitters Per Zone by Emitter Flow

The table below gives emitters per zone from supply divided by emitter flow. Use it when you design a zone from the supply end, before you count rows.

Supply (L/h)	Emitters per zone at 1 L/h	Emitters per zone at 2 L/h	Emitters per zone at 4 L/h
500	500	250	125
1000	1000	500	250
2000	2000	1000	500

The verified figure sits in the middle row. A 1,000 L/h supply runs about 500 emitters of 2 L/h, 1,000 emitters of 1 L/h, and 250 emitters of 4 L/h. Halving emitter flow doubles emitters per zone.

Use this table to set a ceiling for each zone. If your supply is 500 L/h and you use 2 L/h emitters, put no more than 250 emitters in one zone.

The Imperial Tables in Gallons Per Hour

The imperial example uses six 30 ft rows at 12 in spacing, which need 180 emitters and 90 gph. That flow implies an emitter flow of 0.5 gph, because 90 divided by 180 is 0.5, but the page does not state that figure. The metric and imperial examples are separate rounded equivalents, not exact conversions.

The table below uses 0.5 gph emitters for every layout, so total flow is emitters times 0.5. Other rows are example layouts worked through the same formulas. Only the row with 180 emitters is the verified planner example.

Layout	Emitters	Total flow (gph)	Zones at 100 gph	Zones at 250 gph	Zones at 500 gph
Small bed	100	50	1	1	1
Planner example, six 30 ft rows	180	90	1	1	1
Medium rows	300	150	2	1	1
Large rows	600	300	3	2	1
Very large rows	1000	500	5	2	1
Extra large rows	1500	750	8	3	2

Read the imperial table the same way as the metric table. A large layout at 300 gph needs 3 zones on a 100 gph supply and 1 zone on a 500 gph supply. An extra large layout at 750 gph needs 8 zones on a 100 gph supply and 2 zones on a 500 gph supply.

The table below gives emitters per zone in imperial units, from supply divided by emitter flow.

Supply (gph)	Emitters per zone at 0.5 gph	Emitters per zone at 1 gph	Emitters per zone at 2 gph
100	200	100	50
250	500	250	125
500	1000	500	250

A 250 gph supply runs 500 emitters of 0.5 gph, 250 emitters of 1 gph, and 125 emitters of 2 gph. A 500 gph supply runs 1,000 emitters of 0.5 gph and 250 emitters of 2 gph. Use metric or imperial, but do not mix them in one calculation.

Why the Ceil Rule Matters

The ceil rule is easy to miss, because most planning maths rounds to the nearest number. Zone maths rounds up every time, because a zone cannot run part of an emitter set at one time and the rest at another time without a second zone.

Take a layout at 1,020 L/h on a 1,000 L/h supply. The division gives 1.02 zones, but 1 zone cannot run 1,020 L/h from a 1,000 L/h supply. The answer is 2 zones.

Take a layout at 2,000 L/h on a 1,000 L/h supply. The division gives exactly 2.0 zones, so the answer is 2 zones. That exact fit is rare, so plan for the ceil result. Split by emitter count, and check each zone against supply divided by emitter flow.

Pressure, Filter and Backflow

Drip works at about 1 to 2 bar, which is 15 to 30 psi, well below normal mains pressure. That is why drip systems usually need a pressure regulator, which holds pressure inside the drip range.

Drip systems usually also need a filter and a backflow preventer. A filter keeps grit out of the small emitter openings. A backflow preventer keeps water in the drip lines from flowing back into the drinking water supply. Fit all three parts before the first zone valve.

Long runs and slopes need pressure compensating emitters. A normal emitter gives more flow at high pressure and less flow at low pressure. The planner gives a run limit of typically up to 60 m, which is 200 ft, for 16 mm tubing, with less length for high flow emitters.

This guide does not size a pump. Pump sizing is a later batch, and the planner page gives no pump sizing figures. This guide also does not give a run time method. Run time figures are the next batch, and the planner page gives no run time figures.

How to Use the Drip Irrigation Planner

The drip irrigation planner takes the same inputs this guide uses: rows, row length, emitter spacing, lines per row, emitter flow and supply flow. Put in your measured supply, and it returns emitters, tubing, total flow and zones.

Use the planner after you measure supply, not before. Print the parts list the planner gives, and check each zone against the emitters per zone table above before you buy.

Common Mistakes

1. Using a guessed supply instead of a bucket test at the tap you plan to use.
2. Rounding zones to the nearest whole number instead of rounding up.
3. Counting 34 emitters on a 10 m row at 30 cm spacing. Floor of 10 divided by 0.30 is 33 emitters per line.
4. Mixing litres per hour with gallons per hour in one calculation.
5. Putting more emitters in a zone than supply divided by emitter flow allows.
6. Skipping the pressure regulator, filter or backflow preventer.
7. Sizing a pump from this guide. The planner gives no pump sizing figures.

Frequently Asked Questions

Q: How many drip zones can my supply feed?
A: Divide total flow by measured supply flow and round up. Total flow is emitters times emitter flow. If the result is 1.2, you need 2 zones.

Q: How many emitters can one zone run?
A: Divide supply flow by emitter flow. A 1,000 L/h supply runs about 500 emitters of 2 L/h.

Q: How do I measure supply flow at the tap?
A: Use a bucket of known size and time how long it takes to fill at the tap you plan to use.

Q: Does a small amount over supply really need another zone?
A: Yes. Zones use ceil, so any amount over supply means another zone.

Q: Do I need a pressure regulator for drip irrigation?
A: Yes, in most cases. Drip works at about 1 to 2 bar, which is 15 to 30 psi, well below normal mains pressure.

Q: Can I use the same zone count for sprinklers and drip?
A: No. Sprinkler zones use sprinkler head flows and different numbers, so work each system from its own figures.