Methodology

Sources reviewed May 2026

How we build and maintain TablespoonToTeaspoon.com: the primary sources we anchor against, what is in scope and out of scope, the explicit calculation formulas behind every conversion, the monthly refresh cadence, and the limitations we acknowledge. For the simpler reference list of sources without the operational detail, see /sources.

Primary sources

Source	Role	What we take from it	Refresh
NIST SP 811 and NIST Handbook 44	Primary: US Customary volume standards	1 US fluid ounce = 29.5735 ml; 1 US tablespoon = 1/2 US fl oz = 14.7868 ml; 1 US teaspoon = 1/3 US tbsp = 4.9289 ml. Source: National Institute of Standards and Technology Special Publication 811 (Guide for the Use of the International System of Units) and NIST Handbook 44 (Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices).	On NIST revision
BIPM SI Brochure	Primary: metric volume definitions	Litre = 1 dm3 = 0.001 m3; millilitre = 10-6 m3 = 1 cm3. Source: Bureau International des Poids et Mesures (BIPM), SI Brochure, 9th edition.	On BIPM revision
BSI / UK Weights and Measures Act 1985	Primary: UK volume standards	1 UK tablespoon = 15 ml exact; 1 UK teaspoon = 5 ml exact; 1 UK fluid ounce = 28.4131 ml. Source: British Standards Institution and the UK Weights and Measures Act 1985. Cross-referenced against the UK Metric Association.	On statute revision
Standards Australia AS 1291	Primary: Australian tablespoon	1 Australian tablespoon = 20 ml exact; 1 Australian teaspoon = 5 ml exact. Established at metrication in 1974 for a clean 4:1 ratio with the 5 ml teaspoon. Source: Standards Australia AS 1291 (Metric units for cookery).	On Standards Australia revision
USDA FoodData Central	Primary: ingredient density	Density values for water, honey, oils, syrups, dairy. URL: fdc.nal.usda.gov. The 1 ml water = 1 g reference comes from here; per-ingredient gram-per-tablespoon values derive by multiplying density (g/ml) by 14.79 ml for the US tablespoon.	Quarterly cross-check
King Arthur Baking Ingredient Weight Chart	Primary: baking ingredient density	Flour (all-purpose levelled 120 g/cup = 8 g/tbsp; scooped 150 g/cup = 10-12 g/tbsp), bread flour, cake flour, sugars (granulated 200 g/cup; brown packed 213 g/cup), butter, cocoa powder, baking powder, vanilla extract. URL: kingarthurbaking.com/learn/ingredient-weight-chart.	Quarterly cross-check
America's Test Kitchen / Cook's Illustrated	Secondary: volume-vs-weight testing	Volume-versus-weight measurement reliability studies, scoop-method vs spoon-and-level variance figures, heaped vs level tablespoon percentage differentials. Referenced for the 25-50% scoop-method variance figure on flour.	On ATK publication
Serious Eats / J. Kenji Lopez-Alt	Primary: kosher salt density	Diamond Crystal kosher salt = 9 g per US tablespoon (hollow pyramid crystals, packs loosely). Morton kosher salt = 15 g per US tablespoon (flat dense flakes). 1.67x density differential. URL: seriouseats.com / The Food Lab.	Annual cross-check
FDA Office of the Commissioner Consumer Health Information	Primary: liquid medicine dosing safety	Kitchen teaspoons vary 2.5 to 7 ml against a 5 ml calibrated medical teaspoon. Studies cited by the FDA show up to 40% of parents measuring children's medicine with kitchen spoons dose incorrectly. Reference for the FDA dosing-error figure throughout the medicine-dosing page.	On FDA guidance update
American Academy of Pediatrics	Primary: paediatric medicine dosing	AAP policy statement (Metric Units and the Preferred Dosing of Orally Administered Liquid Medications) recommends ml-only dosing via oral syringe for all paediatric liquid medicines. Used as the AAP citation on /medicine-dosing.	On AAP statement update
Institute for Safe Medication Practices (ISMP)	Primary: dosing-error reporting	ISMP MedMARx and Quarterly Action Agendas on medication errors involving teaspoon-vs-tablespoon confusion. Reinforces the case for ml-only dosing with calibrated devices.	Quarterly cross-check
NHS UK and the 5 ml medical spoon	Secondary: UK medicine dosing convention	NHS medicines guidance specifies the 5 ml calibrated medical teaspoon for oral liquids and recommends the oral syringe for under-5s. Referenced for UK-context dosing guidance.	On NHS guidance update
UK Metric Association	Secondary: UK metric conversion reference	Cross-reference for the UK 15 ml tablespoon convention and the metric millilitre. Used as a sanity-check secondary source against BSI primaries.	Annual cross-check
OXO Good Grips kitchen scale documentation	Secondary: weighing recommendation	Reference for kitchen-scale recommendation on /. We cite OXO Good Grips for the home-baker scale standard not because we are sponsored by OXO (we are not) but because it is the standard recommendation across the major baking publications.	Annual cross-check

In scope

US Customary tablespoon (14.7868 ml) and teaspoon (4.9289 ml) anchored to NIST SP 811
UK 15 ml tablespoon and 5 ml teaspoon anchored to BSI / UK Weights and Measures Act 1985
Australian 20 ml tablespoon and 5 ml teaspoon anchored to Standards Australia AS 1291
Decimal numerals (0.1 to 2.5 tablespoon) and fractional numerals (1/8, 1/4, 1/3, 1/2, 2/3, 3/4)
Per-ingredient density per tablespoon for common baking and cooking ingredients (King Arthur + USDA)
Salt brand density (Diamond Crystal vs Morton) and recipe-swap math
Kitchen-spoon variance (2.5 to 7 ml household teaspoon) vs calibrated measuring spoon
Liquid-medicine dosing safety per FDA / AAP / ISMP / NHS guidance
UK dessert spoon (10 ml) cross-reference
Cooking-term modifiers (heaped, level, scant, packed, rounded) with percentage differentials per ATK

Out of scope

Individual recipe troubleshooting (refer to your recipe author)
Clinical medication dosing decisions (refer to your pharmacist or product packaging; this site is not medical advice)
Specific brand affiliation (we cite brands by name when they are the reference; no paid placements)
Restaurant production-scale cooking volumes (we cover home and family-cooking quantities)
Sub-millilitre laboratory volume measurement (we round to 0.01 ml where useful)
Imperial vs US fluid-ounce edge cases beyond the noted UK fl oz (28.4131 ml) vs US fl oz (29.5735 ml) difference

Calculation framework

US/UK tablespoon to teaspoon

tsp = tbsp x 3 (US and UK; both use the 3:1 ratio with a 5 ml teaspoon)

2 tbsp x 3 = 6 tsp (= 29.57 ml using NIST 14.7868 ml/tbsp).

Australian tablespoon to teaspoon

tsp = tbsp x 4 (Standards Australia AS 1291; AU tbsp = 20 ml, tsp = 5 ml)

2 AU tbsp x 4 = 8 tsp (= 40 ml).

US tablespoon to ml

ml = tbsp x 14.7868 (NIST SP 811)

1 US tbsp = 14.79 ml; 2 US tbsp = 29.57 ml = 1 US fl oz.

UK tablespoon to ml

ml = tbsp x 15 (BSI; UK tbsp exactly 15 ml)

1 UK tbsp = 15 ml; 2 UK tbsp = 30 ml.

AU tablespoon to ml

ml = tbsp x 20 (Standards Australia AS 1291)

1 AU tbsp = 20 ml; 2 AU tbsp = 40 ml.

Ingredient gram per US tablespoon

g = density (g/ml) x 14.7868 ml

Water (1.000 g/ml) = 14.79 g; honey (1.420 g/ml) = 21.0 g; flour all-purpose (0.54 g/ml levelled, King Arthur) = 8 g.

Salt brand swap (volume held constant)

Morton g = Diamond Crystal g x 1.67 for equal volume; or Diamond Crystal g = Morton g / 1.67

Recipe calls for 1 tbsp Diamond Crystal (9 g). Substitute Morton: use 9 / 1.67 = 5.4 g of Morton (about 1.75 tsp) for equal saltiness.

Decimal tablespoon to teaspoon

Same as integer; tsp = tbsp x 3 (US/UK)

0.2 tbsp x 3 = 0.6 tsp; 0.25 tbsp x 3 = 0.75 tsp (= 1/4 tbsp = 3/4 tsp).

Refresh cadence

Monthly first-business-week pass driven by a single LAST_VERIFIED_DATE constant in the codebase. The constant drives the footer date, the site-wide WebSite JSON-LD dateModified, every per-page Article schema dateModified, and the "Reviewed May 2026" badges on this page and /about. Out-of-cycle refresh triggers:

NIST standards revision (US Customary volume changes)
BIPM SI Brochure update
FDA dosing-safety guidance update (kitchen-spoon variance, ml-only dosing)
AAP policy-statement update on paediatric liquid medicine dosing
King Arthur Baking Ingredient Weight Chart revision
ATK / Cook's Illustrated measurement-method publication
Standards Australia AS 1291 revision
Reader-flagged correction with cited counter-source

Limitations

Density figures are ranges, not point estimates. Flour spoon-and-level vs scoop method differs by 25 to 50 percent per ATK; we present the spread.
Kitchen spoons are not calibrated. Household teaspoons measure 2.5 to 7 ml typical (FDA-cited). We never recommend kitchen cutlery as a measuring tool for medicine.
Australian tablespoon is distinct from US/UK. Confusion between AU 20 ml and US/UK 15 ml is the single most common cross-regional recipe error; we flag it prominently.
US vs UK fluid ounce differs (29.5735 ml vs 28.4131 ml). Recipes converting between US and UK fluid ounces need to account for this 4 percent gap.
Decimal precision matters in baking but not in cooking. We round to 0.01 ml where useful and round to whole millilitres where appropriate.
Salt density brand figures are from Serious Eats / Kenji Lopez-Alt tests; manufacturer specifications may differ slightly. We use the test figures as the consumer-relevant numbers.

Corrections

For corrections, source disagreements, or new primary sources we should be tracking, email us via the contact form at digitalsignet.com. Cite the page URL, the specific figure or claim, the source you are challenging it against, and the source URL. We respond within 5 business days. Substantive corrections trigger an out-of-cycle LAST_VERIFIED_DATE roll.

Do not email for urgent medical or accidental-overdose questions. For suspected overdose, contact your local poison-control service or emergency services (911 in the US; 999 in the UK; NHS 111 for non-emergency UK medical advice).