Quick answer: To convert stones and pounds to kg, turn the whole weight into pounds (stones × 14, plus the extra pounds), then multiply by 0.45359237. For example, 11 st 5 lb is 159 lb, which is 72.12 kg. Each stone adds 6.35 kg and each extra pound adds 0.45 kg.
Most British scales and doctors’ letters write weight as two numbers, such as “9 st 12 lb”, and most calculators cannot take two numbers at once. The converter below accepts both, and the grid lets you read off common weights without typing. It sits alongside the other tools in our weight conversions section.
Stones and pounds to kg
st lb= kg ( lb in total)Leave the pounds box at 0 for a whole number of stones. If you type 14 or more pounds, the converter still works: it simply treats the extra pounds as another stone.
What is the formula for stones and pounds to kg?
Kilograms = (stones × 14 + pounds) × 0.45359237. The bracket gives the total in pounds, and 0.45359237 is the exact number of kilograms in one pound under the Weights and Measures Act 1985.
Worked example for 9 st 12 lb:
- Stones to pounds. 9 × 14 = 126 lb.
- Add the odd pounds. 126 + 12 = 138 lb.
- Pounds to kilograms. 138 × 0.45359237 = 62.60 kg.
An equivalent route is to convert each part separately and add them: 9 stone is 57.15 kg, 12 lb is 5.44 kg, and 57.15 + 5.44 = 62.59 kg. The final digit can differ by 0.01 kg because each part has been rounded, so the single-formula method is slightly more precise. If you are unsure how the two units relate, our explainer on how many pounds are in a stone covers the basics.
Stones and pounds to kg grid
Find your stones in the first column, then read across to the nearest pounds value. All figures are in kilograms, rounded to two decimal places.
| Stones | +0 lb | +4 lb | +7 lb | +10 lb |
|---|---|---|---|---|
| 6 st | 38.10 | 39.92 | 41.28 | 42.64 |
| 7 st | 44.45 | 46.27 | 47.63 | 48.99 |
| 8 st | 50.80 | 52.62 | 53.98 | 55.34 |
| 9 st | 57.15 | 58.97 | 60.33 | 61.69 |
| 10 st | 63.50 | 65.32 | 66.68 | 68.04 |
| 11 st | 69.85 | 71.67 | 73.03 | 74.39 |
| 12 st | 76.20 | 78.02 | 79.38 | 80.74 |
| 13 st | 82.55 | 84.37 | 85.73 | 87.09 |
| 14 st | 88.90 | 90.72 | 92.08 | 93.44 |
| 15 st | 95.25 | 97.07 | 98.43 | 99.79 |
| 16 st | 101.60 | 103.42 | 104.78 | 106.14 |
| 17 st | 107.95 | 109.77 | 111.13 | 112.49 |
| 18 st | 114.31 | 116.12 | 117.48 | 118.84 |
| 19 st | 120.66 | 122.47 | 123.83 | 125.19 |
| 20 st | 127.01 | 128.82 | 130.18 | 131.54 |
Between columns, each extra pound adds 0.45 kg. So 13 st 9 lb is the 13 st 7 lb value plus two pounds: 85.73 + 0.91 = 86.64 kg.
What mistakes do people make converting stones and pounds?
- Typing 11.5 for 11 st 5 lb. 11.5 stone means eleven and a half stone, which is 11 st 7 lb. Entered as a decimal, 11.5 gives 73.03 kg instead of the correct 72.12 kg, nearly a kilogram out.
- Multiplying the pounds by 6.35. Only stones use the 6.35 factor; loose pounds use 0.4536.
- Rounding the factor too hard. Using 6.3 kg per stone loses 0.05 kg per stone, which is 0.75 kg at 15 stone.
- Comparing different scales. A home scale and a clinic scale may disagree slightly, so a small difference after conversion may be the scales, not the maths.
To reverse the process and turn a kilogram reading back into stones and pounds, use our kg to stone and pounds converter. For a weight given purely in pounds, the lb to kg converter is quicker.
How precise does the kg figure need to be?
For body weight, one decimal place (to the nearest 0.1 kg) is plenty. Bathroom scales rarely show more than one decimal place of a kilogram, and a single pound is already 0.45 kg, so quoting a converted weight to three or four decimal places suggests an accuracy the scale never had.
Keep the full factor while you calculate and round only at the end. Rounding the stones and pounds to kilograms separately, then rounding again, is how a 0.01 kg discrepancy creeps in. If the figure is going on a medical or official form, write down exactly what the scale showed in its original units as well as your conversion, so anyone checking can repeat the sum.
Where the weight matters for health, such as working out a BMI, the NHS BMI calculator lets you enter stones and pounds directly. A GP, pharmacist or practice nurse can explain what the result means for you.
Frequently asked questions
What is 10 stone 7 pounds in kg?
10 st 7 lb is 147 lb, which is 66.68 kg.
What is 12 stone 4 pounds in kg?
12 st 4 lb is 172 lb, which is 78.02 kg.
How many kg is one pound?
One pound is exactly 0.45359237 kg, about 454 grams.
Is 11.5 stone the same as 11 stone 5 pounds?
No. 11.5 stone is 11 stone 7 pounds (73.03 kg), while 11 stone 5 pounds is 72.12 kg.
How do I convert stones and pounds to kg without a calculator?
Use the grid above: find the row for your stones and the nearest pounds column, then add 0.45 kg for each extra pound.
Sources
- Weights and Measures Act 1985, section 1: the pound defined as 0.45359237 kg.
- National Physical Laboratory (UK national measurement standards).
- NHS: BMI calculator.