A rectangular dish can sit on the turntable and clear the door yet catch a wall as it turns. Use its maximum outside width and length to calculate the diagonal, then compare it with space around the actual rotation axis. Check cookware and lid suitability separately.
First check the container, lid and cooking mode
Check the labels and instructions for the container, lid and covering in the mode you intend to use. Microwave suitability does not automatically extend to grill, convection or combination modes. The calculation below estimates turning space; it cannot establish safe materials or adequate food cooking.
Record five measurements, including handles and the closed door
Measure with the appliance stopped and cool. Use centimetres throughout; do not close the door on a ruler or operate the appliance with measuring tools inside. If you cannot establish where the closed door’s inner face sits, leave that measurement unknown.
| Symbol | Measure | Easy to miss |
|---|---|---|
| A · outside width | Widest outside width with the lid and handles as used | Body width or capacity in ml is not enough |
| B · outside length | Longest outside length in the same configuration | Include one-sided handles and projecting rims |
| H · total height | Base to the highest lid or handle point | Check headroom from the fitted turntable surface, not the cavity floor |
| R · axis clearance | Shortest horizontal distance from the actual rotation axis to a wall, closed door or projection | Check over the full container height. Do not substitute the tray radius or half the cavity width |
| g · manual clearance | Dish-to-wall clearance required by your own model's manual | Unknown means blank, not zero or a universal default |
Calculate the diagonal and remaining turning space
For outside width A and length B, diagonal d = √(A² + B²). When the centre of that rectangle is aligned with the rotation axis, its corners sweep a radius of d ÷ 2. Measuring a rectangle that encloses handles as well as the body helps account for projections.
Subtract d ÷ 2 from your measured R for the remaining geometric radial space. If the manual specifies a horizontal gap g, also calculate R − d ÷ 2 − g. A positive number still requires checks of height, stable support, permitted load and materials. Zero leaves no room for measurement error; a negative number does not meet the entered envelope and gap.
Rectangular dish rotation calculator
For a centred rectangle in a turntable appliance only; not irregular shapes or flatbed models. A and B give the diagonal. Add known R and g to compare space.
If the calculator is unavailable, use the formula and worked example in this guide.
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Handles change this example by 3.3cm
These are assumed dimensions to explain the calculation, not measurements of a tested product. R is assumed to be 14cm; no manual-required gap g has yet been deducted.
| Measured outline | Swept diameter d | R − d ÷ 2 |
|---|---|---|
| Body only: 20 × 15cm | 25.0cm | 1.50cm |
| With handles: 24 × 15cm | About 28.3cm | About −0.15cm |
Measuring only the body appears to leave room; including the handles changes the result. The first row is not an approval to use the dish. Displayed numbers are rounded, while comparisons use the unrounded calculation.
When this calculation cannot decide fit
If the dish is off-centre, d ÷ 2 is no longer its actual turning radius. A rectangle around an irregular shape may overestimate its outline, so an oversized envelope does not prove actual contact. If the axis or a door/projection position is unknown, calculate only the diagonal and leave fit undecided. Flatbed models need door, height and model-specific checks rather than this rotation calculation.
Try an existing container before buying another
| What happens | Next step |
|---|---|
| Only this dish catches a wall | Transfer to a smaller microwave-suitable dish you already own. Split portions if the cooking instructions allow it. |
| The lid hits the top or a projection | Choose another container whose lid is also permitted. Do not improvise changes to its lid instructions merely to make it fit. |
| A suitable smaller dish also wobbles or will not turn | Once cool, check tray seating, roller ring and debris as the manual directs. Seek official service if the problem remains. |
Do not remove or obstruct the turntable to force in a larger dish. Use a built-in turntable-off function only as your model’s instructions permit. There is no need to heat an empty dish to measure its size.
The next decision
If you do need to replace the appliance, compare installation space and manual requirements as well as the usable interior.
Before Buying an Appliance: Size, Energy Labels, and Manuals
Sources and scope
This guide compares manufacturer guidance and public food-safety information. It reports no physical heating test; the worked dimensions are explicitly hypothetical.