ENGINEERING TOOL · GD&T POSITION
True position and MMC bonus tolerance calculator
Enter X/Y deviations or basic and measured coordinates. Check the diametrical true position, MMC or LMC bonus tolerance, total allowable zone, virtual condition and overall hole or pin acceptance.Runs locally in your browserNo upload. No sign-in. Instant result.
GD&T POSITION CALCULATOR
True position, bonus tolerance and acceptance.
CALCULATED POSITION
⌖ ⌀0.100 Ⓜ · hole
PASS
Actual true position ⌀0.100 mm2 × radial coordinate offset
Bonus tolerance+0.050 mmDeparture from hole MMC
Total allowable position ⌀0.150 mmStated tolerance + usable bonus
Remaining diametrical margin+0.050 mm66.7% of position tolerance used
Allowed radial zone = 0.075 mm
Radial coordinate offset0.050 mm
Feature sizePASS · 10.050 mm
MMC / LMC sizes10.000 / 10.100 mm
MMC virtual condition⌀9.900 mm
Position and feature size both pass.Assumes X/Y are evaluated in the drawing’s correct datum reference frame. Datum shift from MMB is not included.
THE CORE CALCULATION
Position is diametrical. Coordinate error is radial.
MMC, LMC AND RFS
The bonus direction reverses between a hole and a pin.
Maximum material means the feature contains the greatest volume of material: the smallest hole or the largest pin. Least material is the opposite limit.| Controlled feature | MMC size | MMC bonus | LMC size | LMC bonus |
|---|---|---|---|---|
| Hole / internal feature | Minimum permitted size | Actual size − MMC | Maximum permitted size | LMC − actual size |
| Pin / external feature | Maximum permitted size | MMC − actual size | Minimum permitted size | Actual size − LMC |
| RFS / no modifier | No material-condition bonus; the stated position tolerance remains constant. | |||
WORKED HOLE EXAMPLE
⌀10.000–10.100 hole · ⌖ ⌀0.100 Ⓜ · actual ⌀10.050
Hole MMC = 10.000 mm. Bonus = 10.050 − 10.000 = 0.050 mm. Total allowable position = 0.100 + 0.050 = ⌀0.150 mm. If ΔX = 0.030 and ΔY = 0.040 mm, true position = ⌀0.100 mm, leaving 0.050 mm diametrical margin.
SCOPE THAT PREVENTS FALSE PASSES
A simple calculator should stop where the drawing structure begins.
Size is checked first
An oversized hole or undersized pin does not become acceptable merely because the arithmetic produces a large bonus.
Controlled-feature bonus only
MMC/LMC bonus on the toleranced feature is calculated. Datum shift from MMB or LMB is intentionally excluded.
Datum-relative data required
Use deviations from a CMM or inspection setup aligned to the drawing’s correct datum reference frame and basic dimensions.
Advanced controls stay separate
Composite position, projected zones, pattern refinement, noncylindrical zones and functional-gage design require additional interpretation.
TRUE POSITION FAQ
Questions engineers and inspectors ask about bonus tolerance.
How do you calculate true position from X and Y deviations?
For a cylindrical diametrical position zone, calculate the radial coordinate offset as the square root of ΔX squared plus ΔY squared, then multiply by two. True position error equals 2 × √(ΔX² + ΔY²). The factor of two converts the radial offset into the diameter reported against a ⌀ position tolerance.
How is MMC bonus tolerance calculated for a hole?
A hole contains the most material at its smallest permitted size, so the hole MMC size is its lower size limit. With an MMC modifier on the controlled feature, bonus tolerance equals actual hole size minus MMC hole size, provided the actual size remains within its limits.
How is MMC bonus tolerance calculated for a pin?
A pin contains the most material at its largest permitted size, so the pin MMC size is its upper size limit. With an MMC modifier, bonus tolerance equals pin MMC size minus actual pin size, provided the pin still passes its size limits.
What is the total allowable position tolerance at MMC?
Total allowable diametrical position tolerance equals the stated position tolerance at MMC plus the bonus earned by departure from MMC. The actual diametrical true position must not exceed this total, and the feature size must also pass independently.
What is virtual condition for a hole or pin at MMC?
For the common position-at-MMC boundary calculation, an internal feature virtual condition is hole MMC size minus the stated position tolerance. An external feature virtual condition is pin MMC size plus the stated position tolerance. Functional gage design requires the complete drawing and applicable standard, not this number alone.
Does RFS receive bonus tolerance?
No. When position applies regardless of feature size, the stated position tolerance remains constant through the permitted feature-size range. The calculator still checks the entered size limits, but it adds no size-related bonus.
Does this calculator include datum shift from MMB?
No. It assumes the X and Y values were already evaluated in the correct datum reference frame. Datum-feature shift at maximum material boundary depends on the datum feature, actual mating envelope, datum order and feature control frame. It must not be added as if it were controlled-feature bonus tolerance.
REFERENCE BASIS