Units and where they come from
Every figure our calculators use that does not come from you, with its source and the date we checked it.
Imperial units are defined in UK law as exact amounts of metric ones, in Schedule 1 to the Weights and Measures Act 1985. We build every conversion from those definitions, so an inch is exactly 2.54 cm because a yard is exactly 0.9144 m and an inch is a 36th of a yard. US units come from the US National Institute of Standards and Technology.
Length, area, volume and weight
| Figure | Value | Source |
|---|---|---|
| A yard in metres | 0.914 m per yard | Weights and Measures Act 1985, Schedule 1 Part VI: YARD = 0.9144 metre. Checked 13 November 2026. |
| Feet in a yard | 3 feet per yard | Weights and Measures Act 1985, Schedule 1 Part VI: Foot = 1/3 yard. Checked 13 November 2026. |
| Inches in a yard | 36 inches per yard | Weights and Measures Act 1985, Schedule 1 Part VI: Inch = 1/36 yard. Checked 13 November 2026. |
| Yards in a mile | 1,760 yards per mile | Weights and Measures Act 1985, Schedule 1 Part VI: Mile = 1760 yards. Checked 13 November 2026. |
| Square yards in an acre | 4,840 square yards per acre | Weights and Measures Act 1985, Schedule 1 Part VI: Acre = 4840 square yards. Checked 13 November 2026. |
| Square metres in a hectare | 10,000 m2 per hectare | Weights and Measures Act 1985, Schedule 1 Part II: Hectare = 100 ares; Are = 100 square metres. Checked 13 November 2026. |
| Litres in a cubic metre | 1,000 litres per m3 | Weights and Measures Act 1985, Schedule 1 Part III: LITRE = a cubic decimetre; Cubic decimetre = 1/1000 cubic metre. Checked 13 November 2026. |
| A UK (imperial) gallon in litres | 4.546 litres per gallon | Weights and Measures Act 1985, Schedule 1 Part VI: GALLON = 4.54609 cubic decimetres. Checked 13 November 2026. |
| A UK pint in litres | 0.568 litres per pint | Weights and Measures Act 1985, Schedule 1 Part IV: Pint = 0.568 261 25 cubic decimetre. Checked 13 November 2026. |
| UK fluid ounces in a pint | 20 fluid ounces per pint | Weights and Measures Act 1985, Schedule 1 Part VI: Fluid ounce = 1/20 pint. Checked 13 November 2026. |
| A pound in kilograms | 0.454 kg per pound | Weights and Measures Act 1985, Schedule 1 Part VI: POUND = 0.453 592 37 kilogram. Checked 13 November 2026. |
| Pounds in a stone | 14 pounds per stone | Weights and Measures Act 1985, Schedule 1 Part VI: Stone = 14 pounds. Checked 13 November 2026. |
| Ounces in a pound | 16 ounces per pound | Weights and Measures Act 1985, Schedule 1 Part VI: Ounce = 1/16 pound. Checked 13 November 2026. |
| Pounds in a ton (long ton) | 2,240 pounds per ton | Weights and Measures Act 1985, Schedule 1 Part VI: Ton = 2240 pounds. Checked 13 November 2026. |
| Kilograms in a tonne | 1,000 kg per tonne | Weights and Measures Act 1985, Schedule 1 Part V: Tonne, metric tonne = 1000 kilograms. Checked 13 November 2026. |
| A US gallon in litres | 3.785 litres per US gallon | NIST Guide to the SI, Appendix B.8: factors for units listed alphabetically gallon (U.S.) to liter (L): 3.785 412 E+00. Checked 13 November 2026. |
| A US fluid ounce in millilitres | 29.574 ml per US fluid ounce | NIST Guide to the SI, Appendix B.8: factors for units listed alphabetically ounce (U.S. fluid) to cubic meter: 2.957 353 E-05. Checked 13 November 2026. |
| Fahrenheit reading at the freezing point used in the conversion | 32 °F | NIST Guide to the SI, Appendix B.9: factors for units listed by kind of quantity t/°C = (t/°F − 32)/1.8 Checked 14 November 2026. |
| Fahrenheit degrees in one Celsius degree | 1.8 | NIST Guide to the SI, Appendix B.9: factors for units listed by kind of quantity t/°C = (t/°F − 32)/1.8 Checked 14 November 2026. |
Stairs and ramps
| Figure | Value | Source |
|---|---|---|
| Smallest rise of a step, private stair (in a home) | 150 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Largest rise of a step, private stair (in a home) | 220 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Smallest going of a step, private stair (in a home) | 220 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Largest going of a step, private stair (in a home) | 300 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Smallest rise of a step, utility stair | 150 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Largest rise of a step, utility stair | 190 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Smallest going of a step, utility stair | 250 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Largest going of a step, utility stair | 400 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Smallest rise of a step, general access stair | 150 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Largest rise of a step, general access stair | 170 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Smallest going of a step, general access stair | 250 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Largest going of a step, general access stair | 400 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, Rise and going. Takes effect 6 April 2013 for use in England. Checked 13 November 2026. |
| Steepest pitch of a private stair | 42 degrees | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1, note 1. Checked 13 November 2026. |
| Twice the rise plus the going: smallest | 550 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1: the normal relationship is 2R + G between 550mm and 700mm. Checked 13 November 2026. |
| Twice the rise plus the going: largest | 700 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Table 1.1: the normal relationship is 2R + G between 550mm and 700mm. Checked 13 November 2026. |
| Headroom over a stair | 2,000 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Paragraph 1.11 and Diagram 1.3: at least 2m. Checked 13 November 2026. |
| Reduced headroom for a loft conversion, at the centre of the stair | 1,900 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Paragraph 1.13 and Diagram 1.4, where there is not enough space for 2m. Checked 13 November 2026. |
| Reduced headroom for a loft conversion, at the side of the stair | 1,800 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Paragraph 1.13 and Diagram 1.4. Checked 13 November 2026. |
| Most risers in a flight, utility stair | 16 risers | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Paragraph 1.18, buildings other than dwellings. Checked 13 November 2026. |
| Most risers in a flight, general access stair | 12 risers | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Paragraph 1.18: 12, and exceptionally up to 16 in small premises. Checked 13 November 2026. |
| Drop beside a stair in a home above which guarding is needed | 600 mm | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Paragraph 1.41. Checked 13 November 2026. |
| Ramp going for gradient point 1 | 2 m | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Diagram 2.1. Between 2m and 10m it is acceptable to interpolate. Checked 13 November 2026. |
| Steepest ramp gradient (1 in N) at that going | 12 1 in | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Diagram 2.1: 1:12 up to 2m, 1:15 at 5m, 1:20 at 10m. Checked 13 November 2026. |
| Ramp going for gradient point 2 | 5 m | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Diagram 2.1. Between 2m and 10m it is acceptable to interpolate. Checked 13 November 2026. |
| Steepest ramp gradient (1 in N) at that going | 15 1 in | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Diagram 2.1: 1:12 up to 2m, 1:15 at 5m, 1:20 at 10m. Checked 13 November 2026. |
| Ramp going for gradient point 3 | 10 m | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Diagram 2.1. Between 2m and 10m it is acceptable to interpolate. Checked 13 November 2026. |
| Steepest ramp gradient (1 in N) at that going | 20 1 in | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Diagram 2.1: 1:12 up to 2m, 1:15 at 5m, 1:20 at 10m. Checked 13 November 2026. |
| A floor this steep or steeper should be designed as a ramp (1 in N) | 20 1 in | Approved Document K: protection from falling, collision and impact, 2013 edition (GOV.UK) Paragraph 2.3, note. Checked 13 November 2026. |