How do I calculate the volume of a protective box?

Answer: Work from internal dimensions. Deduct 2.5 mm twice per axis, then remove the 6 mm floor pad and 8 mm liner before calling the result usable height.

Single hinge or double hinge?

Answer: It follows span. Up to 400 mm one hinge is enough; beyond that two hinges keep droop within 1.5 mm.

Is 0.5 mm cell tolerance necessary?

Answer: For rigid items, yes. Cavity size already varies by 0.8 mm, so inserts sit 0.3 mm under the median; soft goods tolerate 1 mm.

Does a small order need new tooling?

Answer: Not always. Under 200 pieces, colour and divider changes reuse an existing cavity; only a new outline needs a 45 day mould.

Is a five-high stack the limit?

Answer: For a standard body, yes. Higher needs cross ribs in the lid or a unit under 10 kg, and flatness has to be rechecked.

How to Choose a Protective Box: 5 Selection Criteria

Quick answer: Convert the outer footprint into usable internal volume first, then check lid travel and latch position, drop and stack figures, divider tolerance and tooling lead time. Each item should resolve into a number you can verify.

Internal Volume Against Outer Footprint
Lid Opening and Latch Position
Drop and Stack Performance
Foam Dividers and Cell Tolerance
Small-Batch Tooling and Lead Time
FAQ

1. Internal Volume Against Outer Footprint

A 400 x 300 x 150 protective box with 2.5 mm walls loses 5 mm per axis before draft angles. Measured internals come out at 395 x 295 x 132, a usable volume of 78 percent; quoting capacity from the outside overstates it by a third.

Usable height decides fit. A 6 mm foam pad on the floor and an 8 mm liner in the lid leave 118 mm of real space inside a 150 mm box, so treat any quoted volume as a ceiling rather than a promise.

Outer	Internal	Usable height	Volume used
300 x 220 x 120	295 x 215 x 102	88 mm	76 percent
400 x 300 x 150	395 x 295 x 132	118 mm	78 percent
500 x 350 x 180	495 x 345 x 162	148 mm	80 percent

The narrowest point decides fit, not the average: side ribs pull the cavity in by 4 mm, so long items are quoted at the narrowed width.

2. Lid Opening and Latch Position

On a protective box, one hinge carries a span up to 400 mm; beyond that, two hinges and a 105 degree opening stop the lid falling back. On a 400 mm box the free end should droop no more than 1.5 mm when open.

Protective box: black long box lying on blue-painted ground beside a freight truck, pale tiled factory wall with a gold sign and two cameras

Latch position matters more than count. Two latches at 12 kg each, set 40 mm in from the ends, sit over the straight run of the gasket; pushed to the middle, they let both ends lift.

Close the lid and run a hand around the 3 mm lip: even resistance is right, and a soft spot marks a lip that moulded short.

3. Drop and Stack Performance

A protective box is small, so drop energy concentrates. Test at 1.5 m on six faces plus a corner drop; a 6 mm corner radius survives where 3 mm cracks, because the load spreads wider.

Stack five high at 15 kg each for 24 hours with lid deflection under 1.0 mm; above that the second layer stops seating, and a lid warped by 2 mm rocks from the fifth up.

Test	Condition	Accept
Six-face drop	1.5 m, empty	Latches closed, no crack
Corner drop	1.5 m, bottom corner	No whitening
Stack	5 high, 15 kg, 24 h	Deflection under 1.0 mm

4. Foam Dividers and Cell Tolerance

Dividers decide how fast a protective box works. Specify EVA at 30 kg per cubic metre, 4 mm walls and cell tolerance of 0.5 mm on a 6 mm base; foam under 25 kg per cubic metre collapses and neighbouring cells merge.

Protective box: black box standing upright on a table showing its back, folding top handle, telescopic red-grip handle at left, two wheels, sample shelves behind

Set tolerance against moulding: cavity size moves 0.8 mm across a batch, so measure ten boxes and cut inserts 0.3 mm under the median.

5. Small-Batch Tooling and Lead Time

Tooling sets the calendar for a protective box. A mould takes about 45 days and three trial shots, with colour signed off after the second. Minimum order is 200 pieces at ΔE 1.0 instead of the 1.5 allowed in a mixed batch, since a short run has no second batch to hide a colour shift.

On the press side, a 350 t machine on a 95 second cycle suits protective box bodies up to 400 mm. Push the cycle under 80 seconds and walls thicken unevenly, which shows as a lid sitting high on one side.

Stage	Scope	Lead time
Tooling	One mould, trials included	45 days
Trials	3 shots, colour on the second	12 days
Production	200 pieces, ΔE 1.0	18 days

Conclusion

The five criteria form one chain: the outline sets the cavity, the cavity sets the dividers, dividers and lid decide handling speed, drop and stack decide life, tooling decides the schedule. Written as numbers, a protective box becomes easy to compare.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.