CMG GardenNotes #266
Converting Inches to Minutes
Outline:
Calculate the precipitation rate, page 1
Convert inches to minutes, page 2
Sprinkler run time table, page 3
Most gardeners realize that temperatures affect the water needs of lawns and
gardens. The difficulty is that water is usually measured in inches while the
irrigation controller (timer) works in minutes. The challenge is to make minutes
equal to inches so that the correct amount of water is applied to the lawn or garden.
It’s easy to make the conversion. First calculate the precipitation rate for each
irrigation zone. Then convert inches to minutes using the formula or the table.
Calculate the Precipitation Rate
The following steps need to be done for each irrigation zone (or each location you
placed the sprinkler if you’re a “hose dragger”). To do the calculations you will
need 6 identical straight-sided, flat-bottomed cans or cups such as soup, fruit or
vegetable cans. (Do not use short cans like tuna cans as they are too shallow, and
water will splash out.) You will need a ruler, a watch, and paper/pen to record
your findings. Many sod growers and local water providers give out small rain
gauges with a ruler on the side for this measurement. You will need 6 of the same
type.
Steps
1. Place six identical, straight-sided, flat-bottomed cans between sprinkler
heads in the zone.
2. Turn on the sprinklers for exactly ten minutes.
3. Pour all the water into one can.
4. With a ruler, measure the depth of the water in the can. This is your
precipitation rate in inches per hour.
5. Write down the number near your controller for future reference.
6. Repeat steps 1-5 for each irrigation zone.
266-1
Table 1. Conversion of fractions to decimals
1/16
1/8
3/16
1/4
5/16
3/8
7/16
1/2
=
=
=
=
=
=
=
=
.06
.13
.19
.25
.31
.38
.44
.50
9/16
5/8
11/16
3/4
13/16
7/8
15/16
=
=
=
=
=
=
=
.56
.63
.69
.75
.81
.88
.94
Convert Inches to Minutes
Once you know the precipitation rate for each zone, you can look up the run time
in the table or calculate it by using the following formula:
Water to apply (inches)
Run Time (minutes) = -------------------------------------------- x 60 minutes/hr
Precipitation rate (inches/hour)
Example: You have done the above steps and calculated that this sprinkler zone
has a precipitation rate of 1.5 inches per hour. You desire to apply
one-half inch of water.
0.5 inches
Run Time = ------------------ x 60 minutes/hr = 20 minutes
1.5 inches/hr.
You need to calculate this for each zone. Don’t make the common mistake of
assuming that all zones are the same. In the typical yard, they are not!
266-2
Table 2. Sprinkler Run Time Table (in minutes) – by 1/8th inch
Precipitation
Rate
Water to be Applied (inches)
(inches
per hour)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1/4
3/8
1/2
48
32
24
72
48
36
96
64
48
120
80
60
144
96
72
168
112
84
192
128
96
216
144
108
240
160
120
264
176
132
288
192
144
312
208
156
336
224
168
360
240
180
5/8
3/4
7/8
1
19
16
14
12
29
24
21
18
38
32
27
24
48
40
34
30
58
48
41
36
67
56
48
42
77
64
55
48
86
72
62
54
96
80
69
60
106
88
75
66
115
96
82
72
125
104
89
78
134
112
96
84
144
120
103
90
1 1/8
1 1/4
1 3/8
1 1/2
11
10
9
8
16
14
13
12
21
19
17
16
27
24
22
20
32
29
26
24
37
34
31
28
43
38
35
32
48
43
39
36
53
48
44
40
59
53
48
44
64
58
52
48
69
62
57
52
75
67
61
56
80
72
65
60
1 5/8
1 3/4
1 7/8
2
7
7
6
6
11
10
10
9
15
14
13
12
18
17
16
15
22
21
19
18
26
24
22
21
30
27
26
24
33
31
29
27
37
34
32
30
41
38
35
33
44
41
38
36
48
45
42
39
52
48
45
42
55
51
48
45
2 1/8
2 1/4
2 3/8
2 1/2
6
5
5
5
8
8
8
7
11
11
10
10
14
13
13
12
17
16
15
14
20
19
18
17
23
21
20
19
25
24
23
22
28
27
25
24
31
29
28
26
34
32
30
29
37
35
33
31
40
37
35
34
42
40
38
36
2 5/8
2 3/4
2 7/8
3
5
4
4
4
7
7
6
6
9
9
8
8
11
11
10
10
14
13
13
12
16
15
15
14
18
17
17
16
21
20
19
18
23
22
21
20
25
24
23
22
27
26
25
24
30
28
27
26
32
31
29
28
34
33
31
30
Select the precipitation rate of your sprinkler zone along the left column and move right until you are in the column of the amount
of water to be applied. This is the number of minutes to run your sprinkler.
Example: Your sprinkler applies water at 1 1/2 inches per hour and you want to apply 0.5 inch, it takes 20 minutes.
266-3
Table 3. Sprinkler Run Time Table (in minutes) – by 1/10th inch
Precipitation
Rate
Water to Be bpplied (inches)
(inches
per hour)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
0.20
0.30
0.40
0.50
60
40
30
24
90
60
45
36
120
80
60
48
150
100
75
60
180
120
90
72
210
140
105
84
240
160
120
96
270
180
135
108
300
200
150
120
330
220
165
132
360
240
180
144
390
260
195
156
420
280
210
168
450
300
225
180
0.60
0.70
0.80
0.90
1.00
20
17
15
13
12
30
26
22
20
18
40
34
30
27
24
50
43
37
33
30
60
51
45
40
36
70
60
52
47
72
80
69
60
53
48
90
77
67
60
54
100
86
75
67
60
110
94
82
73
66
120
103
90
80
72
130
111
97
87
78
140
120
105
93
81
150
129
113
100
90
1.10
1.20
1.30
1.40
1.50
11
10
9
9
8
16
15
14
12
12
22
20
18
17
16
27
25
23
21
20
33
30
28
26
24
38
35
32
30
28
44
40
37
34
32
49
45
42
39
36
55
50
46
43
40
60
55
51
47
44
66
60
55
51
48
71
65
60
56
52
76
76
65
60
56
82
75
69
64
60
1.60
1.70
1.80
1.90
2.00
8
7
7
7
6
11
11
10
9
9
15
14
13
13
12
19
18
17
16
15
22
21
20
19
18
26
25
23
22
21
30
28
27
25
24
34
32
30
28
27
37
35
33
32
30
41
39
37
35
33
45
42
40
38
36
49
46
43
41
39
52
49
47
44
42
56
53
50
47
45
2.10
2.20
2.30
2.40
2.50
6
6
5
5
5
9
8
8
7
7
11
11
10
10
10
14
14
13
12
12
17
16
16
15
14
20
19
18
17
17
23
22
21
20
19
26
25
23
22
22
29
27
26
25
24
31
30
29
27
26
34
33
31
30
29
37
35
34
32
31
40
38
37
35
34
43
41
39
37
36
Select the precipitation rate of your sprinkler zone along the left column and move right until you are in the column of the amount
of water to be applied. This is the number of minutes to run your sprinkler.
Example: Your sprinkler applies water at 1.5 inches per hour and you want to apply 0.5 inch, it takes 20 minutes.
Author: David Whiting, Colorado State University Extension (retired).
o
o
o
o
Colorado Master Gardener GardenNotes are available online at www.cmg.colostate.edu.
Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating.
Extension programs are available to all without discrimination.
Copyright 2002-14. Colorado State University Extension. All Rights Reserved. CMG
GardenNotes may be reproduced, without change or additions, for nonprofit educational use.
Revised October 2014
266-4