How do you calculate sheet utilization?

Multiply the net area of one part by the number of good parts on the sheet, divide by the sheet area and multiply by 100. Thirty 0.833 sq ft parts on a 32 sq ft sheet give 25 / 32 x 100 = 78.1%.

What is a good sheet utilization percentage?

It depends on the part shape. Rectangular parts on a well-matched sheet often reach 85 to 95%; irregular profiles with common-line cutting land around 70 to 85%; round or highly contoured parts can sit below 70%. Compare against your own best nest for the same part rather than a general benchmark.

How do I calculate strip utilization for blanking?

Use the area of one blank divided by the strip area it consumes: blank area / (pitch x strip width) x 100, where the pitch is the feed per stroke. For several blanks per stroke, multiply the blank area by the number of blanks.

How much does the scrap from a nest cost?

Sheet cost x scrap area / sheet area. On an $80 sheet with 7 of 32 sq ft left over, that is $17.50 per sheet before any scrap credit; subtract the scrap value per pound or per ton if you sell the skeleton.

Should I use net area or the part's bounding box?

Net area. The bounding box is useful for laying out the nest, but the material that leaves as product is the net area; using the box makes utilization look better than it is.

Engineering and Process

Sheet Utilization Formula

Sheet utilization is the share of a purchased sheet that ends up in good parts. Use it to compare nests, sheet sizes and blank layouts, and to put a dollar figure on the offcut and skeleton you pay for and scrap.

Formula

Sheet Utilization = (Net Part Area x Accepted Parts) / Sheet Area x 100

Variables

Net Part Area: Area of one finished part, in the same unit as the sheet (holes and cutouts removed)
Accepted Parts: Good parts nested on one sheet
Sheet Area: Area of the purchased sheet, length x width

Understanding the Sheet Utilization Formula

Sheet utilization, also called nesting efficiency or material yield, compares the area that leaves as good parts with the area you bought. In the example, 30 parts of 0.833 sq ft use 25 of the sheet's 32 sq ft, so 78.1% of the sheet is product and 21.9% is skeleton, kerf and offcut.

Use net area, the area of the finished part with holes removed, because that is what actually leaves as product. The same formula serves sheet metal blanking, corrugated and carton blanks, gaskets, wood panels and plastic sheet; strip and coil layouts use the strip pitch times the width as the area per part.

The money is in the remainder. At $80 a sheet, 7 sq ft of scrap is $17.50 per sheet before any scrap credit, so a nest that gains two more parts or a sheet size that fits the pattern better often pays more than a faster machine. Compare layouts on cost per good part, not utilization alone, when a larger sheet costs more per square foot.

Worked Example

A 4 ft x 8 ft sheet (32 sq ft) costing $80 nests 30 parts of 10 in x 12 in, which is 0.833 sq ft each.

Product area = 0.833 sq ft x 30 = 25 sq ft
Sheet utilization = 25 / 32 x 100 = 78.1%
Offcut and skeleton = 32 - 25 = 7 sq ft
Cost of that material = $80 x 7 / 32 = $17.50 per sheet

Result: 78.1% utilization, with $17.50 of each $80 sheet in offcut and skeleton

Common Mistake

Using the part's bounding rectangle instead of its net area. A part with holes or a profile fills less of its rectangle than it appears to, so the rectangle overstates utilization and understates what the scrap costs.

Frequently Asked Questions

How do you calculate sheet utilization?: Multiply the net area of one part by the number of good parts on the sheet, divide by the sheet area and multiply by 100. Thirty 0.833 sq ft parts on a 32 sq ft sheet give 25 / 32 x 100 = 78.1%.
What is a good sheet utilization percentage?: It depends on the part shape. Rectangular parts on a well-matched sheet often reach 85 to 95%; irregular profiles with common-line cutting land around 70 to 85%; round or highly contoured parts can sit below 70%. Compare against your own best nest for the same part rather than a general benchmark.
How do I calculate strip utilization for blanking?: Use the area of one blank divided by the strip area it consumes: blank area / (pitch x strip width) x 100, where the pitch is the feed per stroke. For several blanks per stroke, multiply the blank area by the number of blanks.
How much does the scrap from a nest cost?: Sheet cost x scrap area / sheet area. On an $80 sheet with 7 of 32 sq ft left over, that is $17.50 per sheet before any scrap credit; subtract the scrap value per pound or per ton if you sell the skeleton.
Should I use net area or the part's bounding box?: Net area. The bounding box is useful for laying out the nest, but the material that leaves as product is the net area; using the box makes utilization look better than it is.