Size Ratio Calculator: The Short Answer
A brand orders 600 hoodies in two colours, in sizes S to XL, with a ratio of 1 to 2 to 2 to 1. The size ratio calculator adds the parts (six), divides 600 by six to get 100 pieces per part and returns 100 small, 200 medium, 200 large and 100 extra large. Split evenly across the two colours, that is 50, 100, 100 and 50 in each. The sum is exactly 600, and that is the point of a good ratio tool: when the division is not clean, it still allocates whole pieces that add up to the total you asked for.
The ratio in the example is an illustration, not advice. Which sizes a brand needs depends on who buys it, and the right split usually comes from sales data, a past order or a trial run, which the size ratio calculator then turns into numbers.
The calculator is also a quick way to test how fragile a split is. Change the quantity by a few dozen and watch which cells move. A split that works at 600 pieces may leave a 12-piece cell at 150, and you want to know that before you send the order, not when the factory asks.
Use the Size Ratio Calculator
Enter the total pieces in the order and the number of colours. Then give each size a number of ratio parts: 1, 2, 2, 1 means a quarter, a half, and so on. Leave a size at zero to exclude it. The size ratio calculator splits the total into whole pieces per size and, if there is more than one colour, into a grid of colours by size, with totals that match the order quantity.
Size ratio calculator
Pieces per size and colour
The ratio is your own input and is not a recommendation: the right split depends on your customers. Colours are split evenly.
Try a few ratios against the same quantity. Notice how a wider run, with XS and XXL included, shrinks the smallest cells quickly, which matters when a factory has a minimum per size or colour. Our guide to size ratios for a first production order explains how to choose one.
How a Size Ratio Works
A size ratio expresses each size as a number of parts out of the total. Add the parts, divide the order quantity by that sum to find the pieces per part and multiply by each size's parts. When the division is exact, you are finished. When it is not, you have to round, and how you round decides whether the sizes still add up to the order.
From order quantity to pieces per size
- 1Choose the ratioParts for each size, for example 1 : 2 : 3 : 3 : 2 : 1.
- 2Add the partsThe sum of all size parts.
- 3Find the pieces per partOrder quantity ÷ total parts.
- 4MultiplyPieces per part × parts for each size.
- 5Round to whole piecesAllocate the leftovers so the sizes add to the total.
- 6Split by colourDivide each size across the colours.
A common mistake is to round each size separately. With three equal sizes and 50 pieces, each size is 16.67, and rounding each to 17 gives 51 pieces, one more than ordered. The calculator avoids it by giving the extra piece to the size with the largest remainder, so the answer is 17, 17 and 16.
Why Separate Rounding Goes Wrong
The table shows the rounding trap with the smallest possible example: 50 pieces split equally across three sizes. Each size is exactly 16.67 pieces, so rounding each one separately gives 17, and the three add up to 51.
Rounding each size separately against the largest-remainder method
| Size | Exact share | Rounded separately | Largest remainder |
|---|---|---|---|
| S | 16.67 | 17 | 17 |
| M | 16.67 | 17 | 17 |
| L | 16.67 | 17 | 16 |
| Total | 50.00 | 51 | 50 |
Arithmetic: 50 ÷ 3 = 16.67 pieces per size. The largest-remainder method gives the extra piece to the first size in a tie. Illustrative example.
With bigger orders and uneven ratios the error is rarely so obvious, but it still happens, and a size ratio calculator that always adds up removes it. The same logic splits each size across colours.
A Six-Size Example at Different Order Sizes
The table applies one ratio, XS to XXL in parts of 1, 2, 3, 3, 2 and 1, to four order sizes. The ratio is illustrative and is not a recommendation. Each row is whole pieces and adds up to the order total.
Pieces per size for a 1 : 2 : 3 : 3 : 2 : 1 ratio
| Order quantity | XS | S | M | L | XL | XXL |
|---|---|---|---|---|---|---|
| 300 | 25 | 50 | 75 | 75 | 50 | 25 |
| 600 | 50 | 100 | 150 | 150 | 100 | 50 |
| 1,000 | 83 | 167 | 250 | 250 | 167 | 83 |
| 1,200 | 100 | 200 | 300 | 300 | 200 | 100 |
Calculated with the largest-remainder method so each row sums to the order. The ratio is an illustrative example, not a recommended split.
In the 500-piece case, which is not in the table, 500 divided by twelve parts leaves remainders that the calculator shares out as 42, 83, 125, 125, 83 and 42. Whatever the quantity, the sizes always add up. For help choosing the sizes to offer, see our guide to garment grading and size charts.
How the 600 Pieces Divide
The pie shows the 600-piece order split by the six-size ratio. The middle sizes hold half the order, and the extreme sizes together hold a sixth.
Share of 600 pieces by size at a 1 : 2 : 3 : 3 : 2 : 1 ratio
- XS (50)8.3%
- S (100)16.7%
- M (150)25%
- L (150)25%
- XL (100)16.7%
- XXL (50)8.3%
Arithmetic: 600 ÷ 12 parts = 50 pieces per part. Illustrative ratio, not a recommendation.
The small slices are where the trouble lies. A tiny cell, such as 50 pieces of XS across all colours, can fall below a factory's minimum for a size, so ask about it before you set the ratio. Our guide to minimum order quantities explains where these limits come from.
What Happens to the Smallest Size as the Order Grows
The smallest cell is the one that decides whether a ratio works. The chart shows XS in each of two colours, with a one-in-twelve share, as the order grows from 600 to 4,800 pieces.
Pieces of XS in each of two colours by order size (1 of 12 parts)
Pieces
Arithmetic: order ÷ 12 parts ÷ 2 colours. Illustrative ratio, not a recommendation.
At 600 pieces each colour carries only 25 XS, which is a small cutting lot. At 4,800 it carries 200. If the minimum per size and colour is a problem, the options are a narrower size run, fewer colours or a larger order. The calculator shows each of those in seconds.
Splitting by Colour
Colours multiply the number of cells in an order, and each cell is a cutting lot. A 600-piece order in two colours has eight cells for four sizes, and the same order in four colours has sixteen, each half the size. Dyed fabric often has its own minimum per colour, so more colours can mean fewer pieces in each than the fabric supplier will accept.
An even split across colours is a starting point. If one colour is likely to outsell the others, weight it, but keep the total per size equal to the figure the ratio gave. The size ratio calculator splits evenly because that is the neutral case, and you can adjust the grid by hand once you have it.
Where the Ratio Should Come From
A ratio is a forecast of who will buy. The best source is your own history: what sold, by size, in a similar style. A first-time brand has none, and has to lean on the customers it is aiming at, a small test run or a supplier's experience, and then correct it with the first reorder. Treat the first ratio as a hypothesis.
Sources for a size ratio, from best to weakest
- Your own sales by size for a similar style
- Pre-orders or a waiting list with size choices
- A small test run, read by size sell-through
- Returns data, which shows sizes that did not fit
- Advice from your supplier on similar programmes
- A general guess, to be corrected with the first reorder
A general ranking. Standards bodies such as ISO and ASTM International publish sizing standards; they describe sizes, not who buys them.
Once the first order sells, the sell-through rate calculator shows which sizes cleared and which did not, and the return rate calculator shows what the sizes cost you in returns.
Common Mistakes in a Size Split
The mistakes are few, and each is cheap to avoid before the order is placed.
Sound habits and common slips
Habits that help
- Checking that every size and colour cell meets the factory minimum
- Letting the ratio sum to exactly the order quantity
- Separating the fit decision from the size split
- Recording the ratio and the reasons behind it
Slips to avoid
- Rounding each size separately and ordering the wrong total
- Copying a ratio from another brand without checking the fit
- Spreading a small order across too many colours
- Leaving out the sizes that returns data says you need
Qualitative guidance. Your own sales and fit data decide the split.
Fit matters as much as the ratio. A size that fits badly will sell badly whatever its share, and our UK clothing size chart guide sets out how sizes are labelled.
How Ruhrose Helps You Plan a Size Split
Ruhrose develops hoodies, fleece, jersey, denim and woven casualwear for UK buyers, with production in Bangladesh. We talk through size splits, minimums per size and colour, and how to read the first order, and we sample before bulk so the fit is settled before the ratio is. Ruhrose's clothing manufacturing pages show what we make.
Before you finalise a size split, ask yourself one question: what is the evidence for each number?