Inches Of Water Per Week To mm Per Day Converter
Convert irrigation depth from inches per week to millimetres per day, with area, weekly volume and reverse conversion included.
Convert Irrigation Depth
Converted Water Depth
1 in/week equals 3.6 mm/day.
Quick Conversion
One inch of water is exactly 25.4 mm. Spread over seven days, 1 inch per week is 25.4 / 7, or about 3.63 mm per day. The reverse is also useful: 1 mm per day is about 0.276 inches per week. Irrigation advice from older garden books, US turf references or agricultural notes may use inches per week, while UK rainfall and many irrigation controllers use millimetres. This converter keeps both weekly depth and daily depth visible so the schedule is easier to compare.
Formula And Volume Method
mm per week = inches per week x 25.4mm per day = mm per week / 7inches per week = mm per day x 7 / 25.4Net weekly depth = converted weekly depth - rainfall creditLitres for area = net mm x area m2 / efficiency decimalm3 for area = litres / 1000A depth of 1 mm over 1 m2 equals 1 litre of water. That makes area calculations simple. If a 100 m2 lawn needs 25.4 mm in a week, the theoretical water volume is 2,540 litres. At 80% application efficiency, the gross water needed is about 3,175 litres. Efficiency can be lower with wind drift, poor sprinkler overlap, run-off or evaporation. Rainfall credit is subtracted before the volume is calculated, but only count rain that actually reaches and stays in the root zone.
Inches Per Week To mm Per Day Table
| Inches Per Week | mm Per Week | mm Per Day | 100 m2 Weekly Volume |
|---|---|---|---|
| 0.25 | 6.35 | 0.91 | 635 litres |
| 0.50 | 12.70 | 1.81 | 1,270 litres |
| 0.75 | 19.05 | 2.72 | 1,905 litres |
| 1.00 | 25.40 | 3.63 | 2,540 litres |
| 1.25 | 31.75 | 4.54 | 3,175 litres |
| 1.50 | 38.10 | 5.44 | 3,810 litres |
| 1.75 | 44.45 | 6.35 | 4,445 litres |
| 2.00 | 50.80 | 7.26 | 5,080 litres |
| 2.50 | 63.50 | 9.07 | 6,350 litres |
| 3.00 | 76.20 | 10.89 | 7,620 litres |
Where The Unit Appears
Inches per week often appears in irrigation rules of thumb, especially for lawns, turf and garden beds. Millimetres per day is more convenient for daily controllers and rainfall records. A daily number can be misleading if it is applied too literally. Many soils benefit from deeper, less frequent watering rather than a tiny daily sprinkle. Containers, seedlings, sandy soil and hot greenhouse conditions may need different treatment. Use the conversion to compare advice, then set the real schedule from soil moisture and plant response.
Worked Irrigation Example
A gardener sees advice to apply 1.5 inches of water per week. The converter multiplies 1.5 by 25.4 to get 38.1 mm per week. Dividing by seven gives 5.44 mm per day. For a 60 m2 bed, the weekly theoretical volume is 38.1 x 60, or 2,286 litres. If the system is 75% efficient, the gross amount is about 3,048 litres. If 10 mm of useful rainfall has already fallen that week, the net irrigation depth falls to 28.1 mm before the volume is worked out.
Related Irrigation Reference Conversions
| Reference | Equivalent | Use Note |
|---|---|---|
| 1 mm over 1 m2 | 1 litre | Volume shortcut. |
| 10 mm over 1 m2 | 10 litres | Small bed planning. |
| 25.4 mm | 1 inch | Exact length conversion. |
| 1 inch per week | 3.63 mm/day | Common irrigation reference. |
| 1 mm/day | 7 mm/week | Daily controller setting. |
| 5 mm/day | 35 mm/week | High summer example. |
| 100 litres over 10 m2 | 10 mm | Water butt check. |
| 1 m3 over 100 m2 | 10 mm | Metered water planning. |
| 25 mm rainfall | 25 litres per m2 | Rain gauge comparison. |
| 50% efficiency loss | Double gross water | Poor sprinkler placement. |
These references are helpful when moving between rain gauges, water meters and garden instructions. They also show why watering a large area can use more water than expected. A single 25 mm week over 100 m2 is 2,500 litres before losses.
Sprinkler Timing Check
To turn depth into minutes, place straight-sided containers across the watered area and run the sprinkler for a known time. If the average catch is 6 mm in 20 minutes, the sprinkler applies about 18 mm per hour in those conditions. You can then compare the target weekly depth with the real catch rate. Repeat the test after moving a sprinkler, changing pressure or adding a hose splitter. Uneven catch readings usually mean overlap, pressure or wind matters more than the unit conversion.
For drip irrigation, use emitter flow rates instead of catch cups. Add the litres per hour from all emitters, compare that with the required weekly litres, and then divide by the number of watering sessions. This keeps bed irrigation and container irrigation from being mixed together. Record pressure changes if several taps run at once.
FAQs
How many mm per day is 1 inch per week?
1 inch per week is 25.4 mm per week. Dividing by seven gives about 3.63 mm per day.
How do I convert mm per day to inches per week?
Multiply mm per day by seven, then divide by 25.4. For example, 5 mm/day is about 1.38 inches per week.
Does rainfall count against irrigation?
Useful rainfall can reduce the irrigation amount, but not all rain reaches the root zone. Run-off, shelter and dry soil can reduce the benefit.
How many litres is 1 mm over 1 m2?
It is 1 litre. That is why millimetres are useful for calculating irrigation volume over an area.
Can I water every day with the daily value?
The daily value is an average. Many plants and soils need watering in fewer, deeper sessions rather than daily shallow watering.
Does this include hosepipe restrictions?
No. Check your local water company and council information during dry periods before setting an irrigation plan.
Sources
- National Institute of Standards and Technology. (2008). Guide for the Use of the International System of Units. NIST Special Publication 811. https://www.nist.gov/pml/special-publication-811
- International Bureau of Weights and Measures. (2019). The International System of Units (SI), 9th ed. BIPM. https://www.bipm.org/en/publications/si-brochure
- Royal Horticultural Society. (n.d.). Watering plants. RHS. https://www.rhs.org.uk/garden-jobs/watering