Choose attachment ratio, primary products sold, or secondary products sold under Solve for. Enter the two known values for the same reporting period and select Calculate.

Compare related primary and secondary unit sales over the same period. More than one secondary unit per primary unit can produce a ratio above 100%.

Use consistent units. Fractions can represent divisible products or planning estimates.

Attachment Ratio Formula

The attachment ratio compares secondary unit sales with related primary unit sales, expressed as a percentage. It is not necessarily the percentage of buyers purchasing an add-on.

AR = (S / P) × 100
  • AR = attachment ratio as a percentage
  • S = number of secondary products sold
  • P = number of primary products sold

To calculate the number of secondary products sold, rearrange the formula:

S = P × (AR / 100)

To calculate the number of primary products sold, rearrange the formula:

P = S / (AR / 100)
  • Calculate attachment ratio: Use this when you know the primary products sold and secondary products sold.
  • Calculate secondary products sold: Use this when you know the primary products sold and the attachment ratio.
  • Calculate primary products sold: Use this when you know the secondary products sold and the attachment ratio.

Attachment Ratio Interpretation

Performance benchmarks depend on the products and sales process. These illustrative ranges describe secondary units per 100 primary units; they are not universal performance ratings.

Attachment Ratio Secondary units per 100 primary units Example Meaning
0% to 10% 0 to 10 Up to 10 secondary units per 100 primary units.
10% to 30% 10 to 30 10 to 30 secondary units per 100 primary units.
30% to 60% 30 to 60 30 to 60 secondary units per 100 primary units.
60% or higher 60 or more 60 or more secondary units per 100 primary units; the ratio can exceed 100%.

The next table shows the relationship between primary product sales, attachment ratio, and expected secondary product sales.

Primary Products Sold Attachment Ratio Secondary Products Sold
100 10% 10
100 25% 25
250 20% 50
500 40% 200

Attachment Ratio Examples

Example 1: Calculate attachment ratio

You sold 400 primary products and 80 secondary products.

AR = (80 / 400) × 100 = 20%

The attachment ratio is 20%.

Example 2: Calculate secondary products sold

You sold 750 primary products and have an attachment ratio of 12%.

S = 750 × (12 / 100) = 90

The number of secondary products sold is 90.

Attachment Ratio FAQ

What does attachment ratio mean?

Here, attachment ratio is secondary units sold divided by primary units sold, multiplied by 100. For example, 25 secondary units for 100 primary units gives 25%. This need not mean 25% of customers bought an add-on, because a customer may buy multiple units.

Can an attachment ratio be over 100%?

Yes. An attachment ratio can be over 100% if more than one secondary product is sold per primary product. For example, if 100 primary products are sold and 140 secondary products are sold, the attachment ratio is 140%.

Is attachment ratio the same as conversion rate?

No. Attachment ratio compares secondary product sales to primary product sales. Conversion rate usually compares completed purchases, signups, or actions to total visitors, leads, or opportunities.