What this calculator works out
This calculator multiplies surface area by the number of coats and divides by the paint's coverage rate, giving the millilitres required.
It works from measured area rather than a proxy, which makes it more reliable than a length-based estimate — provided you can measure or estimate the area.
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Before you calculate
- Coverage in square centimetres per millilitre comes from the manufacturer where stated, or from experience. 50 to 70 cm² per ml is a reasonable range for brushed acrylics.
- Estimate area by breaking the subject into rectangles and cylinders rather than trying to be exact.
- Airbrushing roughly halves the effective coverage because of overspray.
- Primer and varnish have their own coverage rates and should be calculated separately.
Several thin coats give a better finish than one thick one — sharper detail, fewer brush marks and less risk of obscuring fine surface features. They also use slightly less paint in total, because a thick coat pools and is wasted in recesses. More coats is not more paint.
How this calculator works
Area times coats, divided by coverage:
Millilitres = surface area × coats ÷ coverage in cm² per mlThe calculation assumes uniform coverage. In practice, recesses, undersides and awkward angles take more, and the figure should be treated as a minimum rather than a target.
Worked example: 400 cm²
Using the default figures — 400 cm² with 2 coats at 60 cm² per ml:
- Paint required: 13.33 ml
Under a single 17 ml pot, comfortably. Halve the coverage to 30 cm² per ml — a reasonable allowance for airbrushing — and it becomes 26.7 ml, or two pots. That doubling is the single largest variable in modelling paint quantities, and it is why airbrush users buy paint in larger bottles.
Common mistakes
- Using brush coverage for airbrushing. Overspray roughly halves it.
- Applying one thick coat. It obscures detail and wastes paint in recesses.
- Forgetting primer and varnish. Each is a separate quantity.
- Overestimating coverage. Manufacturer figures assume ideal conditions.
- Ignoring the recesses. Uniform coverage is an assumption, not an outcome.
Frequently asked questions
How do I estimate a model's surface area?
Break it into simple shapes. A fuselage is roughly a cylinder — circumference times length. Wings are roughly rectangles, counted on both faces. Adding 20% for the awkward remainder gives a workable figure. Precision is not needed, since paint is bought in whole pots.
Why do thin coats work better?
Thick paint pools in panel lines and recesses, softening the detail the kit's manufacturer moulded in, and it dries with visible brush texture. Thin coats build colour gradually, preserve detail and level out as they dry. The trade is patience — each coat needs to dry before the next.
Does primer really help?
Yes, on almost every subject. It gives the colour coats something to key to, reveals seams and blemishes while they can still be fixed, and provides a uniform base so the colour looks the same over plastic, filler and photo-etch. Skipping it is the most common cause of a finish that looks patchy for no obvious reason.
How much thinner do I need?
For airbrushing, commonly between 10% and 50% of the paint volume depending on the paint and the pressure. It is worth calculating separately, because thinner is consumed faster than most modellers expect and running out mid-session stops work.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- Health and Safety Executive — spray painting, ventilation and respiratory protection
- GOV.UK — chemical labelling and safe disposal
Sources are checked at publication and can change — how I choose and check references.