Granite Surface Plate Grades Explained: 00, 0, 1 and 2, and How to Choose the Right Size
Granite surface plate grades are the first thing a buyer should understand before requesting a quotation, because the grade decides the flatness tolerance, the price, and whether the plate can actually support the measurements you plan to make on it. Yet grade tables are often quoted from memory, mixed across standards, or copied without checking which size they apply to.
This guide explains what grades 00, 0, 1 and 2 mean, gives indicative flatness tolerances for common plate sizes, and then walks through which grade fits which working scenario. It closes with calibration intervals and daily maintenance, so you can plan the purchase and the lifetime cost together. One note before the numbers: grading systems such as DIN 876 and GB/T 20428 follow the same logic but are not interchangeable documents. The exact tolerance for your plate depends on its size and the standard version applied, and the binding figure is always the one printed on the calibration certificate delivered with the plate.
What a grade actually specifies
A grade is a flatness tolerance class for the working surface. It does not describe the material, the surface finish, or the stand — those are specified separately. Flatness means the total distance between the highest and lowest points of the working surface, measured over the whole area in a controlled-temperature room with calibrated equipment.
Grades are arranged so that each step down roughly doubles the allowed tolerance. Grade 00 is the most accurate and the most expensive to lap and verify; grade 2 is the most tolerant and the most economical. There is no single “best” grade — a grade 2 plate that is used within its tolerance is a better purchase than a grade 00 plate that drifts unchecked on a shop floor.
Indicative flatness tolerances by grade and size
The table below gives typical total flatness tolerances in micrometres for common plate sizes, following the grading logic used in DIN 876 and comparable national standards. Treat these as orientation values for purchasing discussions — the exact figures for a specific plate come from the applicable standard version and are confirmed on the inspection certificate.
| Plate size (mm) | Grade 00 | Grade 0 | Grade 1 | Grade 2 |
|---|---|---|---|---|
| 300 × 200 | ~1.5 µm | ~3 µm | ~6 µm | ~12 µm |
| 400 × 250 | ~2 µm | ~4 µm | ~8 µm | ~16 µm |
| 500 × 500 | ~2.5 µm | ~5 µm | ~10 µm | ~20 µm |
| 630 × 400 | ~2.5 µm | ~5 µm | ~10 µm | ~20 µm |
| 800 × 500 | ~3 µm | ~6 µm | ~12 µm | ~24 µm |
| 1000 × 630 | ~3.5 µm | ~7 µm | ~14 µm | ~28 µm |
| 1000 × 1000 | ~4 µm | ~8 µm | ~16 µm | ~32 µm |
| 1600 × 1000 | ~5 µm | ~10 µm | ~20 µm | ~40 µm |
| 2000 × 1000 | ~6 µm | ~12 µm | ~24 µm | ~48 µm |
| 2000 × 1500 | ~6.5 µm | ~13 µm | ~26 µm | ~52 µm |
| 3000 × 2000 | ~9 µm | ~18 µm | ~36 µm | ~72 µm |
Two things stand out in the table. First, tolerance scales with size — a grade 1 large plate can be less flat in micrometres than a grade 2 small plate, and both are correct for their class. Second, the ratio between adjacent grades stays close to two, which is why one grade step makes a visible difference in price: reaching half the tolerance takes more lapping cycles and more verification time.
For plates larger than the sizes listed here, grading is still applied but verification becomes a project of its own — the measurement uncertainty of the lab itself grows with plate size. Our assembly, calibration and inspection service covers large plates and assembled structures, where flatness is verified on site or on calibrated machines rather than assumed from a table.
Which grade fits which scenario
Grade 00 is for reference and calibration work: master plates used to check other plates, calibration laboratories, and applications where the plate itself must contribute almost no error to the measurement. It is also the right choice when the plate will be used with electronic levels, autocollimators or other instruments whose resolution is finer than a few micrometres.
Grade 0 suits inspection rooms and quality departments that verify machined parts with dial indicators, height gauges and comparators. If your part tolerances are in the range of tens of micrometres, a grade 0 plate keeps the reference error a small fraction of the tolerance being checked.
Grade 1 is the workhorse for machine shops: setup, first-article checks, and everyday inspection next to production. Most shop-floor plates fall here, and for most shop-floor measurements that is entirely appropriate.
Grade 2 is for layout, marking, assembly support and rough checks where the plate is a stable, flat, corrosion-free work surface more than a measuring reference. Using grade 2 for final inspection of tight-tolerance parts is where problems begin — the plate may consume a noticeable share of the tolerance band.
A practical selection rule used in many labs: keep the plate’s flatness tolerance to roughly one fifth or less of the tightest tolerance you regularly verify on it. If that ratio cannot be reached within budget, the honest alternatives are a smaller grade 00 plate for critical checks plus a larger lower-grade plate for general work, or tighter control of what gets measured where.
How to choose the right size
Size drives price faster than grade does, because granite is heavy material and lapping time grows with area. Three questions usually settle the size:
First, what has to sit on the plate? The working surface should cover the part plus the measuring equipment with margin — a height gauge needs travel room, a comparator needs its stand fully on the plate. A plate where the part barely fits produces awkward setups and handling risk.
Second, where will it stand? A 2000 × 1000 plate is a substantial object that needs floor space, a proper stand, and access for rigging. If the room cannot give the large plate a stable, level position away from doors, sunlight and HVAC outlets, a smaller plate in a better grade often measures more reliably than a large plate in a poor location.
Third, how heavy are the parts? Load capacity depends on thickness and support, not on grade. Large parts may call for a thicker plate or a surface plate with a matching steel stand designed to carry the load without deflecting the working surface.
For most inspection labs, one main plate in grade 0 or 1 at a size that comfortably fits the largest routine part, plus clear rules about which measurements go on which plate, delivers better results than a single oversized plate bought “to be safe”.
Calibration intervals
There is no universal expiry date on a granite plate; the interval comes from usage and risk. Common practice is to recalibrate every 12 months for plates in daily inspection use, and every 24 months for lightly used reference plates in stable environments. Plates on shop floors with temperature swings, heavy handling or frequent part contact should be checked more often, and any suspected event — an impact, a drop of a heavy part, a move to another room — justifies an unscheduled check.
Calibration should be documented: measurement method, equipment used, room temperature, and the measured flatness against the graded tolerance. When a plate fails its grade after years of wear, re-lapping is normally possible — the material is uniform through its thickness. Our resurfacing service restores the working surface and the plate returns with a fresh certificate at the grade you specify.
Daily maintenance
Granite asks for little, but a few habits protect both the flatness and the finish. Keep the surface clean and dry; wipe off coolant, oil and dust instead of letting them dry on. Never slide abrasive or heavy sharp parts across the surface — lift them, or use soft pads. Do not use the plate as a workbench for hammering, marking or deburring; that is what grade 2 layout plates are for. Keep it away from direct heat sources and sunlight, which create local gradients that temporarily distort readings.
Cover the plate when not in use, and check the support or levelling mounts occasionally — a plate that has gone out of level can appear to have lost flatness when the structure underneath is the real problem. For cleaning agents and handling details, the same rules apply as for other granite measuring equipment: mild, non-aggressive fluids and soft cloths.
Frequently asked questions
Is grade 00 always the right choice?
No. Grade 00 costs significantly more because halving the tolerance takes more lapping and verification time. If your tightest routine measurement is at grade 0 or grade 1 tolerance levels, buying grade 00 adds cost without adding measurement capability. Match the grade to the tolerance you verify, using the one-fifth rule described above.
Are DIN 876, GB/T 20428 and other standards the same?
They follow the same grading logic with grades 00, 0, 1 and 2, but they are separate documents with their own size ranges and tolerance tables. Do not mix tolerance figures from different standards. Ask which standard your plate is certified to, and read the values from that standard’s table and the delivered certificate.
How long does a granite surface plate last?
Decades with normal care. The material does not rust and does not wear measurably under proper use. What usually ends a plate’s service at a given grade is accumulated wear or an impact, and both cases are typically resolved by re-lapping rather than replacement.
Can a dropped grade 1 plate be re-certified as grade 0?
Sometimes. Re-lapping removes a small amount of material and can restore a flatter surface, but whether the plate reaches a higher grade depends on its size, thickness and condition. Send us the plate’s details and the calibration history, and we will assess whether re-lapping to the higher grade is realistic before you commit.
What information should I include in an inquiry?
The working size you need, the grade or the tolerance you must verify, the expected load, the environment (temperature range, humidity), and whether you need a stand. With these details we can propose the grade, size and support as one matched set, and confirm the exact tolerance figures from the applicable standard for your plate.
Summary
Grades 00, 0, 1 and 2 describe how flat the working surface is, with tolerance roughly doubling at each step down, and tolerance also growing with plate size. Choose the grade from the tightest tolerance you actually verify on the plate, choose the size from the parts and equipment that must sit on it, and plan calibration and re-lapping from day one. If you share your part sizes, tolerance requirements and floor conditions, we will recommend a granite surface plate configuration with the exact certified tolerances, rather than leaving you to compare tables from memory.
Post time: Oct-15-2026