The stone is a unit of weight that has a particularly rich history, mainly used in the UK and Ireland for human body weight measurement. Originating from the Biblical days, a stone was once standardized by the British Act of Parliament in 1835 to equal 14 pounds. This peculiar unit is still popular in daily life, especially in conversations about body weight or livestock; any Harry Potter fan will recognize Hagrid’s impressive weight mentioned in stones!
An interesting fact is that the symbol for stone “st” doesn’t change forms, much like “lb” for pounds, which can be confusing at first glance. Unlike metric units with their straightforward conversions, the cultural and historical essence of the stone makes it an intriguing part of British heritage, fostering a sense of continuity from medieval markets to modern times.
The kilogram, the base unit of mass in the International System of Units (SI), has a fascinating history tied to a physical artifact. Until 2019, it was defined by Le Grand K, a platinum-iridium cylinder stored in a vault in France. However, even slight surface contamination or material wear could alter its mass. To ensure a more stable and universally consistent measure, the kilogram is now defined by the Planck constant—a fundamental constant of nature—using a Kibble balance. This revolutionary change marked a significant milestone in metrology and brings mass measurement into line with other SI units that are already defined by fundamental constants, rather than physical objects.
| Stones | Kilograms |
|---|---|
0
st
|
0
kg
|
0.5
st
|
3.17515
kg
|
1
st
|
6.35029
kg
|
1.5
st
|
9.52544
kg
|
2
st
|
12.70059
kg
|
2.5
st
|
15.87573
kg
|
3
st
|
19.05088
kg
|
3.5
st
|
22.22603
kg
|
4
st
|
25.40117
kg
|
4.5
st
|
28.57632
kg
|
5
st
|
31.75147
kg
|
5.5
st
|
34.92661
kg
|
6
st
|
38.10176
kg
|
6.5
st
|
41.27691
kg
|
7
st
|
44.45205
kg
|
7.5
st
|
47.6272
kg
|
8
st
|
50.80235
kg
|
8.5
st
|
53.97749
kg
|
9
st
|
57.15264
kg
|
9.5
st
|
60.32779
kg
|
10
st
|
63.50293
kg
|
10.5
st
|
66.67808
kg
|
11
st
|
69.85322
kg
|
11.5
st
|
73.02837
kg
|
12
st
|
76.20352
kg
|
12.5
st
|
79.37866
kg
|
13
st
|
82.55381
kg
|
13.5
st
|
85.72896
kg
|
14
st
|
88.9041
kg
|
14.5
st
|
92.07925
kg
|
15
st
|
95.2544
kg
|
15.5
st
|
98.42954
kg
|
16
st
|
101.60469
kg
|
16.5
st
|
104.77984
kg
|
17
st
|
107.95498
kg
|
17.5
st
|
111.13013
kg
|
18
st
|
114.30528
kg
|
18.5
st
|
117.48042
kg
|
19
st
|
120.65557
kg
|
19.5
st
|
123.83072
kg
|
20
st
|
127.00586
kg
|
20.5
st
|
130.18101
kg
|
21
st
|
133.35616
kg
|
21.5
st
|
136.5313
kg
|
22
st
|
139.70645
kg
|
22.5
st
|
142.8816
kg
|
23
st
|
146.05674
kg
|
23.5
st
|
149.23189
kg
|
24
st
|
152.40704
kg
|
24.5
st
|
155.58218
kg
|
25
st
|
158.75733
kg
|
25.5
st
|
161.93248
kg
|
26
st
|
165.10762
kg
|
26.5
st
|
168.28277
kg
|
27
st
|
171.45792
kg
|
27.5
st
|
174.63306
kg
|
28
st
|
177.80821
kg
|
28.5
st
|
180.98336
kg
|
29
st
|
184.1585
kg
|
29.5
st
|
187.33365
kg
|
30
st
|
190.5088
kg
|
30.5
st
|
193.68394
kg
|
31
st
|
196.85909
kg
|
31.5
st
|
200.03424
kg
|
32
st
|
203.20938
kg
|
32.5
st
|
206.38453
kg
|
33
st
|
209.55967
kg
|
33.5
st
|
212.73482
kg
|
34
st
|
215.90997
kg
|
34.5
st
|
219.08511
kg
|
35
st
|
222.26026
kg
|
35.5
st
|
225.43541
kg
|
36
st
|
228.61055
kg
|
36.5
st
|
231.7857
kg
|
37
st
|
234.96085
kg
|
37.5
st
|
238.13599
kg
|
38
st
|
241.31114
kg
|
38.5
st
|
244.48629
kg
|
39
st
|
247.66143
kg
|
39.5
st
|
250.83658
kg
|
40
st
|
254.01173
kg
|
40.5
st
|
257.18687
kg
|
41
st
|
260.36202
kg
|
41.5
st
|
263.53717
kg
|
42
st
|
266.71231
kg
|
42.5
st
|
269.88746
kg
|
43
st
|
273.06261
kg
|
43.5
st
|
276.23775
kg
|
44
st
|
279.4129
kg
|
44.5
st
|
282.58805
kg
|
45
st
|
285.76319
kg
|
45.5
st
|
288.93834
kg
|
46
st
|
292.11349
kg
|
46.5
st
|
295.28863
kg
|
47
st
|
298.46378
kg
|
47.5
st
|
301.63893
kg
|
48
st
|
304.81407
kg
|
48.5
st
|
307.98922
kg
|
49
st
|
311.16437
kg
|
49.5
st
|
314.33951
kg
|
50
st
|
317.51466
kg
|
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