Backpack rain-cover sizing calculator

Calculate required clearance-expanded pack dimensions and usable cover minus required dimensions, by axis with your own figures.

Your numbers

Use the units shown. Results update as you change valid inputs.

Use required clearance-expanded pack dimensions and usable cover minus required dimensions, by axis to compare changes to your inputs. The method and limits below explain the scope.

Examples

Examples

Try the starting example

Loaded pack bounding-box width, height, depth (cm)
30,60,25
Measured usable interior cover-box width, height, depth (cm)
35,65,30
Supplied clearance on each side of each axis (cm)
2
Required clearance-expanded pack dimensions (cm)
34, 64, 29
Usable cover minus required dimensions, by axis (cm)
1, 1, 1
All supplied axis margins nonnegative
Yes
Smallest supplied dimensional margin (cm)
1

Try another scenario

Loaded pack bounding-box width, height, depth (cm)
30,65,25
Measured usable interior cover-box width, height, depth (cm)
35,65,30
Supplied clearance on each side of each axis (cm)
2
Required clearance-expanded pack dimensions (cm)
34, 69, 29
Usable cover minus required dimensions, by axis (cm)
1, -4, 1
All supplied axis margins nonnegative
No
Smallest supplied dimensional margin (cm)
-4
Calculation method

Calculation method

Required clearance-expanded pack dimensions (cm)

For each fixed-orientation axis use pack dimension+2×clearance.

Usable cover minus required dimensions, by axis (cm)

Subtract expanded required dimensions from measured usable interior cover dimensions.

All supplied axis margins nonnegative

Yes only when every signed dimensional margin≥0.

Smallest supplied dimensional margin (cm)

Minimum of the three axis margins; negative is an exceeded axis.

Symbols and units
a
Loaded pack bounding-box width, height, depth (cm)
b
Measured usable interior cover-box width, height, depth (cm)
c
Supplied clearance on each side of each axis (cm)

Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.

Assumptions & limits

Assumptions & limits

  • A fixed-orientation rectangular bounding-box comparison using measured usable interior dimensions. Flexible fabric shape, attachment, closure and waterproof coverage are not modeled; advertised nominal volume alone is not a usable interior box.
Are these inputs private?

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Further reading

OpenStax: ratios and rates; all itinerary rates, limits and scenario rules are supplied inputs ↗

Background reading; this does not imply endorsement or independent review of SumFizz.

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