How do I add ounces when the total goes past 16?

Add the ounces on their own first. If the total reaches 16 or more, carry one pound for every whole 16 ounces and keep the remainder. Adding 3 lb 12 oz and 2 lb 9 oz gives 12 + 9 = 21 ounces; 21 is over 16, so carry 1 lb and keep 5 oz, then add the pounds: 3 + 2 + 1 carried = 6 lb. The answer is 6 lb 5 oz. That is how to add ounces without losing the carry, and if you leave both pounds fields at zero the page works as a straightforward add oz calculator.

How do you subtract pounds and ounces when the ounces are too small?

You borrow, exactly as you would when subtracting ordinary numbers — except a pound is worth 16, not 10. For 5 lb 4 oz minus 2 lb 9 oz you cannot take 9 from 4, so borrow one pound and turn it into 16 ounces: 5 lb 4 oz becomes 4 lb 20 oz. Now 20 − 9 = 11 oz and 4 − 2 = 2 lb, giving 2 lb 11 oz. Used as a subtract lbs and oz calculator, this page shows that borrow as its own step rather than jumping to the answer.

Does it handle both adding and subtracting?

Yes — the two buttons at the top switch between them, so one tool covers pounds and ounces calculator subtraction as well as addition. The rule is the same in both directions: addition carries across the 16-ounce boundary, subtraction borrows across it. You can also keep pressing "Add another weight" to total or deduct more than two items at once.

What happens if the weight I subtract is heavier?

The result is negative, and this calculator says so plainly rather than hiding the minus sign or flipping the numbers silently. Subtracting 5 lb 8 oz from 2 lb 3 oz gives −3 lb 5 oz, which is another way of saying the second weight is heavier than the first by 3 lb 5 oz.

Is a pound always 16 ounces?

For everyday weight, yes — the avoirdupois pound used for groceries, postage, body weight and freight is exactly 16 ounces. Precious metals are the exception: a troy pound is 12 troy ounces, and a troy ounce is heavier than an ordinary one, so the two pounds are not the same weight. Fluid ounces are a different thing again, measuring volume rather than weight.

Are the weights I enter sent anywhere?

No. The whole calculation runs in your browser on your own device. Nothing is uploaded, nothing is stored, and the page keeps working offline once it has loaded.

Lbs and Oz Calculator: Add and Subtract Pounds and Ounces

Enter two or more weights and this calculator for pounds and ounces will add or subtract them, carrying and borrowing across the 16-ounce boundary the way you were taught at school — and showing every step. It also gives you the total in decimal pounds, in ounces, and in kilograms and grams. Everything runs in your browser.

Result —

Total ounces—

Decimal pounds—

Kilograms—

Grams—

The working

How pounds and ounces arithmetic actually works

A lb and oz calculator has to do something an ordinary one cannot, and it is worth seeing why. Weight in the US customary system is written in two units at once, and that is the whole difficulty. A pound is exactly 16 ounces — not 10, not 100 — so the moment you add or subtract two weights you are doing arithmetic in base 16 for the right-hand column and base 10 for the left. Punch 5.4 − 2.9 into an ordinary calculator when you meant 5 lb 4 oz − 2 lb 9 oz and you get 2.5, which is not the answer in any unit at all.

There are two reliable ways through it. The first is the schoolbook method of carrying and borrowing across the 16-ounce boundary, which is what this tool displays step by step so you can follow or check it. The second is to convert everything to ounces, do one plain subtraction, and convert back — which is what the code does internally, because a single integer is impossible to get wrong. Both give the same answer; the first is the one you can do on paper.

Adding pounds and ounces: the carry method

Adding lbs and oz is a two-column job. Add the ounces column first, then the pounds column, and if the ounces come to 16 or more you carry the excess over as whole pounds. That one rule is the whole of what an adding pounds and ounces calculator does internally.

To add pounds and ounces by hand, take 3 lb 12 oz + 2 lb 9 oz. The ounces give 12 + 9 = 21 oz. That is past 16, so one whole pound is carried and 21 − 16 = 5 oz stays behind. Now the pounds: 3 + 2, plus the 1 carried, = 6 lb. The answer is 6 lb 5 oz — or 101 ounces, or 6.3125 lb, or 2.8633 kg.

When the ounces come to less than 16 there is nothing to carry and the two columns stay independent: 1 lb 5 oz + 2 lb 6 oz is simply 3 lb 11 oz. The case worth watching is when they land on exactly 16 — 4 lb 10 oz + 1 lb 6 oz gives 16 oz, which carries a full pound and leaves zero, so the answer is a clean 6 lb 0 oz rather than the "5 lb 16 oz" that a careless carry produces.

If all you have is a column of ounces, leave every pounds field at zero and use this as a plain add ounces calculator: adding ounces on their own is the same operation with one column switched off, and the total still rolls up into pounds as soon as it passes 16. An adding lbs and oz calculator and an adding ounces calculator are the same machine underneath — the second is just the first with the pounds column left empty.

Subtracting pounds and ounces: the borrow method

Subtracting pounds and ounces is the same idea running backwards, and it is where most people go looking for a weight subtraction calculator, because the borrowing is easy to fumble. If the ounces you are taking away are larger than the ounces you have, borrow one pound from the pounds column and add 16 to the ounces column — not 10, which is the single most common slip.

The worked example: 5 lb 4 oz − 2 lb 9 oz. You cannot take 9 oz from 4 oz, so borrow a pound. That pound is worth 16 oz, so 5 lb 4 oz is rewritten as 4 lb 20 oz. Now both columns subtract cleanly: 20 − 9 = 11 oz, and 4 − 2 = 2 lb. The result is 2 lb 11 oz, which is 43 ounces, 2.6875 lb, or 1.219 kg.

When no borrowing is needed the sum is quicker than it looks — 9 lb 11 oz − 3 lb 4 oz is just 6 lb 7 oz. And borrowing still works when the ounces column is zero: 6 lb 0 oz − 2 lb 8 oz becomes 5 lb 16 oz − 2 lb 8 oz = 3 lb 8 oz.

Press Subtract and the tool works as a subtract pounds and ounces calculator on any pair of weights you type in — the same job a subtracting lbs and oz calculator does, since lb and lbs, oz and ounces, are only the short and long spellings of the same units. It borrows automatically and prints the step, so you can check the answer by hand rather than take it on trust. Subtracting lbs and oz across several items works the same way: add more rows and each is taken off the running total in turn.

When the second weight is heavier

A subtraction can go below zero, and a subtracting pounds and ounces calculator that quietly swaps the inputs to avoid showing a minus sign is lying to you. Subtracting 5 lb 8 oz from 2 lb 3 oz gives −3 lb 5 oz: in ounces that is 35 − 88 = −53, and 53 oz is 3 lb 5 oz. This tool prints the negative result and also says it in words — that the second weight is heavier than the first by 3 lb 5 oz — because when you are comparing a parcel against a shipping limit, the direction of the difference is the thing you actually needed to know.

Adding more than two weights

You can keep adding rows, which is the normal case when you are totalling a box of items rather than comparing two of them. Three parcels of 1 lb 9 oz, 2 lb 11 oz and 14 oz give 9 + 11 + 14 = 34 ounces, which is 2 lb 2 oz once you carry, on top of 1 + 2 = 3 lb — a total of 5 lb 2 oz, or 82 ounces. In subtract mode the first weight is the starting amount and every row beneath it is taken away, which is how you check what is left of an allowance after several deductions.

Common weights in pounds and ounces

Every figure in this table is computed from the exact definitions, not rounded off a chart.

Weight	Total ounces	Decimal pounds	Kilograms	Grams
0 lb 1 oz	1	0.0625	0.0283	28.35
0 lb 4 oz	4	0.25	0.1134	113.40
0 lb 8 oz	8	0.5	0.2268	226.80
0 lb 12 oz	12	0.75	0.3402	340.19
1 lb 0 oz	16	1	0.4536	453.59
1 lb 8 oz	24	1.5	0.6804	680.39
2 lb 0 oz	32	2	0.9072	907.18
3 lb 0 oz	48	3	1.3608	1360.78
5 lb 0 oz	80	5	2.2680	2267.96
7 lb 8 oz	120	7.5	3.4019	3401.94
10 lb 0 oz	160	10	4.5359	4535.92
16 lb 0 oz	256	16	7.2575	7257.48
50 lb 0 oz	800	50	22.6796	22679.62

Two shortcuts are worth memorising: one ounce is 0.0625 lb, and a quarter pound is 4 oz. Going the other way, a kilogram is about 2 lb 3.27 oz, and a stone — still used for body weight in Britain and Ireland — is 14 lb, or 224 oz, or 6.3503 kg.

Where you actually need this

Postage and shipping. US domestic parcel rates are banded by the ounce at the light end and by the pound above that, so the difference between 12.1 oz and 13 oz is a real price change — carriers round a part-ounce up to the next whole one. Working out whether a padded envelope plus its contents clears a threshold is a lb-and-oz subtraction.

Baby weight. Newborns in the US are recorded in pounds and ounces, and weight gain is tracked in ounces, so parents and midwives are constantly subtracting one reading from another. A baby who was 7 lb 8 oz at birth — 120 oz, or 3.4019 kg — and is 8 lb 3 oz a fortnight later has gained 11 oz. Fractions of an ounce are common on hospital scales, so this calculator accepts decimals such as 6.5 oz.

Cooking and recipes. American recipes give dry weights in pounds and ounces, and scaling a recipe up or down means combining them. Note that an ounce of flour is a weight while a fluid ounce of milk is a volume — the two are not interchangeable, and a recipe that mixes them catches people out constantly.

Freight, luggage and gear. Airline allowances, courier limits and backpacking base weights are all quoted in pounds and ounces, and the useful question is nearly always a subtraction: how much headroom is left before the limit. That is precisely what a subtract weight calculator is for — enter the allowance first, then everything already packed.

Avoirdupois ounces and troy ounces are not the same

Almost everything weighed in daily life uses the avoirdupois system, where a pound is 16 ounces and an ounce is exactly 28.349523125 g. Precious metals use the troy system instead, where an ounce is 31.1034768 g — about 2.75 g heavier, or roughly 10% more.

The trap is the pound. A troy pound is only 12 troy ounces, so it comes to 373.2417 g against the ordinary pound’s 453.59237 g — the troy ounce is heavier, yet the troy pound is lighter. An avoirdupois ounce is about 91.15% of a troy ounce. If you are weighing gold or silver, a pound and ounce calculator built on the avoirdupois system is the wrong tool; for grocery, postage, body and freight weight, it is exactly the right one.

Common mistakes

Borrowing 10 instead of 16. The reflex from decimal arithmetic is hard to suppress and it produces an answer 6 oz light every time.

Treating 5 lb 4 oz as the number 5.4. The decimal form of 5 lb 4 oz is 5.25 lb, because 4 oz is a quarter of a pound. Writing weights as decimals is fine, but only after dividing the ounces by 16 — never by moving a decimal point.

Leaving 16 or more ounces in the answer. "5 lb 16 oz" is not wrong so much as unfinished; it should be 6 lb 0 oz. Any answer with 16 or more ounces still has a carry in it.

Confusing ounces with fluid ounces. One measures mass, the other volume, and they only coincide by accident for a few liquids.

Frequently asked questions

How do I add ounces when the total goes past 16?: Add the ounces on their own first. If the total reaches 16 or more, carry one pound for every whole 16 ounces and keep the remainder. Adding 3 lb 12 oz and 2 lb 9 oz gives 12 + 9 = 21 ounces; 21 is over 16, so carry 1 lb and keep 5 oz, then add the pounds: 3 + 2 + 1 carried = 6 lb. The answer is 6 lb 5 oz. That is how to add ounces without losing the carry, and if you leave both pounds fields at zero the page works as a straightforward add oz calculator.
How do you subtract pounds and ounces when the ounces are too small?: You borrow, exactly as you would when subtracting ordinary numbers — except a pound is worth 16, not 10. For 5 lb 4 oz minus 2 lb 9 oz you cannot take 9 from 4, so borrow one pound and turn it into 16 ounces: 5 lb 4 oz becomes 4 lb 20 oz. Now 20 − 9 = 11 oz and 4 − 2 = 2 lb, giving 2 lb 11 oz. Used as a subtract lbs and oz calculator, this page shows that borrow as its own step rather than jumping to the answer.
Does it handle both adding and subtracting?: Yes — the two buttons at the top switch between them, so one tool covers pounds and ounces calculator subtraction as well as addition. The rule is the same in both directions: addition carries across the 16-ounce boundary, subtraction borrows across it. You can also keep pressing "Add another weight" to total or deduct more than two items at once.
What happens if the weight I subtract is heavier?: The result is negative, and this calculator says so plainly rather than hiding the minus sign or flipping the numbers silently. Subtracting 5 lb 8 oz from 2 lb 3 oz gives −3 lb 5 oz, which is another way of saying the second weight is heavier than the first by 3 lb 5 oz.
Is a pound always 16 ounces?: For everyday weight, yes — the avoirdupois pound used for groceries, postage, body weight and freight is exactly 16 ounces. Precious metals are the exception: a troy pound is 12 troy ounces, and a troy ounce is heavier than an ordinary one, so the two pounds are not the same weight. Fluid ounces are a different thing again, measuring volume rather than weight.
Are the weights I enter sent anywhere?: No. The whole calculation runs in your browser on your own device. Nothing is uploaded, nothing is stored, and the page keeps working offline once it has loaded.

Sources

NIST Special Publication 811 — Guide for the Use of the International System of Units (SI), 2008 edition (PDF) — the conversion tables in Appendix B, and footnote 22, which states that the exact factor for the avoirdupois pound is 4.535 923 7 × 10⁻¹ kg. The same tables give the avoirdupois ounce as 2.834 952 × 10¹ g and the troy ounce as 3.110 348 × 10¹ g, which are the constants this page uses.
NIST — Special Publication 811 landing page — the publication record for the guide above, including its current status and errata.
Federal Register, 1 July 1959 (PDF) — Refinement of Values for the Yard and the Pound — the notice that fixed 1 pound (avoirdupois) = 0.453 592 37 kilogram exactly, bringing the US, UK, Canada, Australia, New Zealand and South Africa into agreement. It also records that the previous 1894 value was 0.453 592 4277 kg, about 1 part in 10 million heavier.
NIST Office of Weights and Measures — Approximate conversions from US customary measures to metric — the everyday rounded equivalents (an ounce as 28.35 g, a pound as 0.45 kg) for sanity-checking the exact figures above.