Stone to Kilogram Converter
Convert mass between stones and kilograms in either direction using the exact international-pound relationship behind the standard stone.
Mass input
Nonnegative decimal mass; use a period for decimals. Grouped thousands such as 1,250 are accepted.
Edit this field to reverse the conversion from kilograms to stones. Scientific notation is intentionally rejected.
Edit either field. The field you most recently type in becomes the source value, and the other field is recalculated immediately.
Live conversion
How to use this stone to kilogram calculator
What this calculator does
This calculator converts a mass between stones (st) and kilograms (kg). It is designed for ordinary unit conversion, including body-mass records, shipping notes, historic or UK-style measurements, and any calculation where one source gives mass in stones while another expects kilograms. The conversion is an exact unit identity when the modern international avoirdupois pound is used: one stone is 14 pounds and one pound is exactly 0.45359237 kilograms, so one stone is exactly 6.35029318 kilograms. The calculator converts the number you enter; it does not measure mass, assess health, or determine whether a particular weight is appropriate.
When to use it
- Convert a body-weight reading recorded in stones into kilograms for a metric form or log.
- Translate a historical, sporting, travel, or personal record that uses stones into SI units.
- Reverse a kilogram value into stones when comparing figures reported in different unit systems.
How to calculate
- The calculator opens with a complete demonstration: 15 stones and its exact converted value, so the results and Download Excel action are usable immediately.
- To convert stones to kilograms, replace the value in Weight in stones. To reverse the calculation, type into Weight in kilograms. The field you edit most recently becomes the source.
- Read Converted result for the rounded four-decimal answer, then use the Stones, Kilograms, and Exact conversion factor cards for the normalized values and factor.
- Select Download Excel to create a current-state XLSX workbook with Summary and Inputs sheets. Select Reset to clear both demonstration values and all calculated results. After Reset, Excel export remains unavailable until you enter a complete valid value again.
Input guide
Weight in stones is an editable, nonnegative decimal mass in st and is the natural source when converting stone to kg. When this is the field you last edited, it is the required source; the kilogram field is then derived automatically. The supported range is 0 through 1,000,000,000,000 st. Enter a plain decimal such as 15 or a correctly grouped value such as 1,250.5. A period is the decimal marker. Values below zero, scientific notation such as 1e3, malformed grouping, and ambiguous decimal-comma forms such as 1,5 are rejected. Increasing the stone value increases kilograms in direct proportion.
Weight in kilograms is the reverse editable source in kg. When it is the field you last edited, it is the required source and the stone field is derived. The supported range is 0 through 1,000,000,000,000 kg. A realistic example is 100 kg, which converts to about 15.7473 st. It follows the same format and validation rules as the stone field. Entering a higher kilogram value produces a proportionally higher stone value. A common mistake is to type both units into the field; enter the number only because the unit is already shown beside the control.
Output guide
Converted result is the main answer and changes direction according to the field you last edited. It is displayed to four decimal places. Stones and Kilograms show the same canonical mass in each unit; both are exact conversions of one another before display rounding. A zero source produces zero in the other unit. Exact conversion factor is the fixed identity 6.35029318 kg/st, not an estimate or user-adjustable assumption.
Worked example
The startup example uses 15 st. Multiply 15 by 6.35029318 kg/st: 15 × 6.35029318 = 95.2543977 kg. The primary result rounds that to 95.2544 kg, matching the four-decimal presentation used throughout the live result. In reverse, dividing 95.2543977 kg by 6.35029318 returns exactly 15 st apart from normal floating-point representation.
Learn more
The kilogram is the SI base unit of mass; the BIPM definition of the kilogram explains how it is defined in the modern International System of Units. For consistent notation, NIST also publishes practical guidance on writing SI metric units and decimal values.
How the stone-to-kilogram conversion works
The stone is an avoirdupois mass unit equal to 14 pounds. The international avoirdupois pound is exactly 0.45359237 kg, so multiplying by 14 gives the exact modern conversion factor used here:
For the reverse direction, divide kilograms by 6.35029318, which is the same as multiplying by approximately 0.1574730444 st/kg. A NIST publication on U.S. mass standards states that the avoirdupois pound is defined as exactly 0.45359237 kg; see the NIST Journal of Research discussion of mass standards. Because the conversion is linear, doubling a mass in stones doubles the kilogram result, and halving it halves the result.
Accuracy, rounding, and common mistakes
The calculator keeps the exact factor 6.35029318 in its internal model and rounds only for display where appropriate. That distinction matters when a converted value is reused in another calculation: the XLSX workbook stores the canonical numeric value rather than a rounded screen string. Four displayed decimals are more than enough for most everyday conversions, while the exact factor remains visible for auditability.
Do not confuse mass with force: kilograms and stones are mass units. Also avoid chaining conversions from a rounded intermediate when precision matters. For example, converting 15 st to 95.25 kg and then back to stone introduces a small rounding difference that is not part of the unit identity. Enter the original value into this calculator instead. Finally, use a period as the decimal separator here; the parser deliberately rejects ambiguous forms rather than silently changing their meaning.