EDUCATIONAL AND PSYCHOLOGICAL MEASUREMENT
1970, 30, 607-610.
DETERMINING SAMPLE SIZE FOR RESEARCH
ACTIVITIES
ROBERT V. KREJCIE
University of Minnesota, Duluth
DARYLE W. MORGAN
Texas A. & M. University
The ever increasing demand for research has created a need for an efficient method of
determining the sample size needed to be representative of a given population. In the article
“Small Sample Techniques,” the research division of the National Education Association has
published a formula for determining sample size. Regrettably a table has not bee available for
ready, easy reference which could have been constructed using the following formula.
s = X 2 NP (1 − P) ÷ d 2 ( N − 1) + X 2 P(1 − P).
s = required sample size.
X2 = the table value of chi-square for 1 degree of freedom at the desired confidence level
(3.841).
1.96 x 1.96 = 3.8416
N = the population size.
P = the population proportion (assumed to be .50 since this would provide the maximum
sample size).
d = the degree of accuracy expressed as a proportion (.05).
No calculations are needed to use Table 1. For example, one may wish to know the
sample size required to be representative of the opinions of 9000 high school teachers relative to
merit pay increases. To obtain the required sample size enter Table 1 at N = 9000. The sample
size representative of the teachers in this example is 368. Table 1 is applicable to any defined
population.
The relationship between sample size and total population is illustrated in Figure 1. It
should be noted that as the population increases the sample size increases at a diminishing rate
and remains relatively constant at slightly more than 380 cases.
REFERENCE
Small-Sample Techniques. The NEA Research Bulletin, Vol. 38 (December, 1960), p. 99.
TABLE 1
Table for Determining Sample Size from a Given Population
N
S
10
10
15
14
20
19
25
24
30
28
35
32
40
36
45
40
50
44
55
48
60
52
65
56
70
59
75
63
80
66
85
70
90
73
95
76
100
80
110
86
120
92
130
97
140
103
150
108
160
113
170
118
180
123
190
127
200
132
210
136
Note.—N is population size.
S is sample size.
N
220
230
240
250
260
270
280
290
300
320
340
360
380
400
420
440
460
480
500
550
600
650
700
750
800
850
900
950
1000
1100
S
140
144
148
152
155
159
162
165
169
175
181
186
191
196
201
205
210
214
217
226
234
242
248
254
260
265
269
274
278
285
N
1200
1300
1400
1500
1600
1700
1800
1900
2000
2200
2400
2600
2800
3000
3500
4000
4500
5000
6000
7000
8000
9000
10000
15000
20000
30000
40000
50000
75000
1000000
S
291
297
302
306
310
313
317
320
322
327
331
335
338
341
346
351
354
357
361
364
367
368
370
375
377
379
380
381
382
384