5 Stones to Pounds

Five stone is 70 pounds, and the 14 does all the work

Five stone is 70 pounds. The arithmetic is one line: 5 x 14 = 70. The stone has meant 14 pounds since Schedule 1 of the Weights and Measures Act 1985 listed it between the quarter and the cental, and that schedule is still the legal definition used in Britain.

Kilograms take one more step. The international pound is 0.45359237 kg, the factor printed in NIST SP 811, Appendix B.8, so 70 x 0.45359237 = 31.7514659 kg. Ounces are 70 x 16 = 1120 oz, and grams are 31751.4659 g.

The stone is a counting word, not a separate measure. It says how many groups of 14 to gather, then leaves the sentence. A 70 pound child, a 70 pound suitcase and a 70 pound sack of sand are one weight, and a metric scale shows 31.75 kg for each of them.

Two displays of that weight turn up in daily use. British scales print 5 st 0 lb. American scales print 70.0 lb. Both are exact names for the mass, and the 0.0485341 kg that a 31.8 kg display adds on top of the true figure is 48.53 g.

Half stone marks: 63, 70, 77 and 84 pounds

British bathroom scales step in half stones, and a half stone is 7 pounds. Around five stone the four marks read 63, 70, 77 and 84 pounds.

The pound column climbs by 7 and the kilogram column by 3.17514659. That second step is half of 6.35029318 kg, the weight of one stone, so the two columns cannot drift apart.

Half marks are what most people read first. A needle between 5 st and 5 st 7 lb is somewhere in the low seventies, and a reading of 5 st 3 lb (73 pounds) is a quarter of the way from 70 to 77. Gym scales in Britain often carry a stone dial and a kilogram dial side by side, and the two dials disagree by up to half a pound because each one rounds its own mechanism.

The 84 pound mark earns its place for a second reason. It is 6 stone, and 6 x 14 = 84 repeats the pattern one step up. Nothing in the mechanism changes at that point; only the label does.

5 st 7 lb is 77 pounds: where the odd pounds go

A British scale rarely stops on a whole stone. The reading 5 st 7 lb means five full stones plus seven pounds, so 5 x 14 + 7 = 77 pounds. In kilograms that is 77 x 0.45359237 = 34.92661249 kg, and in ounces 77 x 16 = 1232 oz.

Run the sum backward and the notation explains itself. 77 / 14 = 5 with 7 left over, so 77 pounds is 5 st 7 lb. The remainder is always under 14, which is why nobody writes 5 st 14 lb. That weight is 6 st 0 lb, or 84 pounds.

The table below covers every leftover pound at five stone. The kilogram column moves by 0.45359237 per row and never repeats, so a kilogram reading points back at one row only.

A metric estimate for 77 pounds: multiply by 0.45 and get 34.65, which lands 0.28 kg under the exact 34.92661249. That is fine for a suitcase and not fine for a prescription, so keep the exact factor when the number goes on a form.

Seventy pounds against 20, 23 and 32 kg baggage caps

Airline desks weigh in kilograms, so 70 pounds arrives as 31.75 kg and the allowance decides the rest. A 20 kg cap is 20 / 0.45359237 = 44.09245244 pounds. Seventy pounds is 158.76 percent of that cap, which puts the bag 25.91 pounds, or 11.75 kg, over the line. A 23 kg cap is 50.70632030 pounds, and 70 pounds runs 19.29 pounds past it.

The 32 kg tier is the first one that fits. It converts to 70.54792390 pounds, so a 70 pound bag clears it by 0.55 pound, or 0.25 kg. That margin is smaller than a paperback, and a pair of trainers added at the last minute turns a legal bag into an excess baggage fee.

Pack against the margin, not the cap. On the 32 kg tier there is 0.55 pound to play with, so the bag should leave home at the weight it was measured at. On the 23 kg tier the same bag needs 19.29 pounds removed before it flies, which is more than most people pack for a week.

The 20 kg row explains a common scene at the counter. A traveller who says "it is only five stone" is handing over 31.75 kg to a desk that allows 20 kg. The words sound light because the stone is a large unit, and the fee is calculated on the kilogram figure.

A five stone goal: 70 weeks at 1 lb, 47 at 1.5, 35 at 2

Five stone is a goal people say out loud, and 70 pounds is the size of it. At 1 pound a week the plan runs 70 weeks. At 1.5 pounds a week it runs 46.67 weeks, so a calendar says 47. At 2 pounds a week it runs 35 weeks.

NHS weight loss guidance puts a safe pace at 1 to 2 pounds, or 0.5 to 1 kg, a week. That range turns 70 pounds into 35 to 70 weeks. In metric, 31.7514659 kg at 0.5 kg a week is 63.5 weeks, and at 1 kg a week it is 31.75 weeks.

Weigh the goal against the starting frame before fixing a date. On a 200 pound body, 70 pounds is 35 percent of body weight. On 250 pounds it is 28 percent, and on 180 pounds it is 38.9 percent. The same 70 pounds is a different project on each frame, and a doctor should set the pace when the share is large.

Reading 70 pounds on a gym floor, a parcel label and a doctor's scale

Seventy pounds is a familiar load in a gym. It is a 45 pound bar with a 25 pound plate on it, since 45 + 25 = 70. It is also two 35 pound plates on a machine stack, and a pair of 35 pound dumbbells, which is 15.88 kg each.

Hotel gyms label in kilograms. A 32 kg dumbbell is 70.54792390 pounds, so it sits 0.55 pound above the 70 pound one at home. A 30 kg plate is 66.13867860 pounds, which is 3.86 pounds light of 70. Lifters notice the second one and not the first.

Parcel scales round harder than gym scales. A carrier that bills in whole kilograms turns 31.7514659 kg into 32 kg and charges for 70.55 pounds. A carrier that rounds down bills 31 kg, which is 68.34330128 pounds, and undercharges by 1.66 pounds. Across a 40 box pallet that gap reaches 66 pounds of billable weight.

A doctor's scale in Britain usually shows kilograms to one decimal, so 70 pounds appears as 31.8. The display drops 48.53 g, which is under the tolerance of most mechanical scales. The figure to record is 31.75 kg, and the figure to say out loud is thirty two kilos.

Rounding 31.7514659 to 31.75, 31.8 or 32

31.7514659 carries more digits than any label needs, and each cut can be measured. Cut to 31.75 and the label is 0.0014659 kg light, or 1.47 g. Cut to 31.8 and it is 0.0485341 kg heavy, or 48.53 g. Cut to 32 and it is 0.2485341 kg heavy, which is 248.53 g.

Convert each label back into pounds and the size of the cut shows up in the unit people weigh in. 31.75 / 0.45359237 = 69.99676824 lb. 31.8 / 0.45359237 = 70.10699937 lb. 32 / 0.45359237 = 70.54792390 lb.

The pattern is worth naming: rounding down to 31.75 keeps the error under 0.004 pound, while rounding up to 32 adds more than half a pound. A 0.5 kg label step is 1.1 pound, so a scale with 0.5 kg steps can move a 70 pound reading by more than a pound in either direction.

Write the figure the reader expects. A British reader wants 5 st 0 lb. An American wants 70 lb 0 oz. A shipping form wants 31.7514659 kg. What to avoid is the sentence "five stone is 32 kg", because 32 kg is 70.54792390 pounds and the pound count is the legal anchor.